Abundance index
Information obtained from samples or observations that is used to measure the weight or number of fish that make up a stock.
Acid rain
Natural rainfall that contains nitric and sulfuric acids due to nitrogen oxide (NOx) and sulfur dioxide discharged into the air by industries, power plants, automobiles and other emission sources.
The science or practice of farming, including growing crops and raising animals for the production of food, fiber, fuel and other products.
Air deposition
An airborne pollutant (often nitrogen) that falls onto the land and runs off into the water, or falls onto the water itself.
The area of land over which airborne pollutants can travel to reach a particular river, lake, bay or other body of water. The Chesapeake Bay’s airshed is 570,000 square miles, stretching north to Canada, west to Ohio and south to South Carolina.
Tiny, single-celled planktonic plants. Algae, or phytoplankton, are the primary producers of food and oxygen in the Bay food web.
Algae bloom
A dense population of algae whose growth is fueled by excess nutrients. Algae blooms can block sunlight from reaching underwater grasses, and their decomposition can rob the water of dissolved oxygen and suffocate marine life.
The amount of pollution a source is allowed to discharge during a given period of time.
A cold-blooded vertebrate that lives in water and on land. Amphibians’ aquatic, gill-breathing larval stage is typically followed by a terrestrial, lung-breathing adult stage. For example, frogs, toads and salamanders are amphibians found in the Chesapeake Bay watershed.
A small, shrimp-like crustacean.
Anadromous fish
Fish that spend their adult lives in salt water but must migrate to freshwater tributaries to spawn. For example, Atlantic sturgeon and American shad are both anadromous fish.
Not containing oxygen or not requiring oxygen.
Someone who fishes recreationally with a hook, line and rod.
A condition in which little or no oxygen is present in a body of water. Also called a “dead zone.”
Caused by humans.
The farming of plants and animals that live in water, such as fish or shellfish.
Living in water.
Aquatic reef
A solid, three-dimensional ecological community made up of densely packed oysters or other natural substances. Aquatic, or oyster, reefs provide vital habitat for finfish, crabs and other invertebrates.
A body of permeable rock that can contain or transmit groundwater.
A group of animals that have four pairs of legs and a body divided into two segments. Spiders, ticks, scorpions and mites are all arachnids.
A diverse group of invertebrates that have jointed legs and an exoskeleton, or external skeleton. Aquatic arthropods include horseshoe crabs and crustaceans like blue crabs and barnacles. Terrestrial arthropods include insects, scorpions and spiders.
Artificial reef
An underwater structure made of artificial substances (such as concrete or metal) that mimics oyster reefs and provides habitat for aquatic species that live on or around aquatic reefs.
Atmospheric deposition
The process by which airborne pollutants settle onto land or water. “Wet deposition” refers to pollutants that fall to the earth while attached to raindrops or snowflakes. “Dry deposition” refers to pollutants that fall to the earth without precipitation.
The process by which forests reduce the amount of pollutants in the air.


A still body of water or a still portion of a larger body of water that is unaffected by the flow of the larger body of water. A small stagnant branch of a river would be considered a backwater.
Water, sand, or other heavy material used to give ships weight and stability.
The portion of river flow that comes from groundwater, rather than runoff.
The numeric level of pollution coming from a source during a particular time period, which is used as a standard to measure future reduction goals and allowances against.
An area of land that drains into a particular river, lake, bay or other body of water. Also called a watershed.
The varying physical characteristics — including depth, contour and shape — of the bottom of the Bay and other bodies of water.
Bay jurisdictions
Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia and the District of Columbia.
Colorful, environmentally sound landscapes that provide wildlife habitat; slow and filter polluted runoff; and require less mowing, fertilizer and pesticides.
Solid rock underlying the earth’s surface.
Bottom-dwelling. Benthic organisms spend at least part of their lives in, on or near the bottom of aquatic environments.
Benthic macroinvertebrate
Bottom-dwelling invertebrates that can be seen with the unaided eye. Benthic macroinvertebrates are used by state and federal water resource agencies to assess stream health.
Plants and animals that live in or on the bottom of an aquatic environment, including worms, shellfish and bottom-feeding finfish.
Best management practices (BMPs)
The most effective and practical ways to control pollutants and meet environmental quality goals. BMPs exist for forestry, agriculture, stormwater and many other sectors.
The uptake and storage of chemical contaminants by living animals and plants. This can occur through direct contact with contaminated water or sediment or through the ingestion of another organism that is contaminated. For example, a small fish might eat contaminated algae, a bigger fish might eat several contaminated fish and a human might eat a bigger, now-contaminated fish. Contaminants typically increase in concentration as they move up the food chain.
The variety of life forms, the ecological roles they perform and the genetic diversity they contain.
Biological diversity
The variety of life in all forms, levels and combinations, including ecosystem diversity, species diversity and genetic diversity.
Biological nutrient removal (BNR)
Wastewater treatment technology that uses microorganisms to remove nitrogen and phosphorous from effluent.
The amount of a living species, expressed as a concentration or weight per unit area.
Bioretention site
Also called a rain garden; an innovative method of stormwater management that retains rainwater and uses plants and layers of soil, sand and mulch to reduce the amount of nutrients and other pollutants that enter local waterways.
The flora and fauna of a region.
An aquatic mollusk whose compressed body is enclosed within a hinged shell. For example, clams, oysters and mussels are bivalves.
A dense population of algae fueled by excess nutrients. Algae blooms rob the Bay's aquatic life of sunlight and dissolved oxygen.
A type of wetland that has poorly drained acidic peat-soil dominated by sedges and sphagnum moss.
A combination of fresh and salt water. Most of the water in the Bay is brackish.
Fish, sea turtles, sea stars and other aquatic animals that are unintentionally caught in fishing gear. Bycatch is usually thrown back into the water dead or dying.


The top layer of a forest. The canopy shades and protects the plants and animals below it, while intercepting and slowing rainfall.
The total amount of nutrients or sediments allowed to be discharged into a given water body. The cap is the baseline minus the pollutant load that needs to be reduced to meet a water quality or restoration goal.
Cap load
The maximum amount of nutrients and sediments that can be allowed to flow into a waterway and still have it meet water quality criteria.
Cap load allocations
Based on each tributary's nutrient and sediment input to the Bay, the total Chesapeake Bay pollution load is divided proportionally to each tributary and jurisdiction. Cap load allocations show where the nutrient and sediment loads will most effectively be reduced to achieve restoration goals.
A hard shell covering the back of an animal, such as a crab or turtle.
An animal or plant that feeds on animal tissue or meat.
The rotting flesh of a dead animal.
Carrying capacity
The maximum number of individual organisms that a habitat or a region can support before environmental degradation or social stress takes place.
Catadromous fish
Fish that spend most of their lives in freshwater tributaries but must migrate to salt water to spawn. The American eel is the only catadromous fish in the Chesapeake Bay region.
A type of mollusk. The brief squid is the only cephalopod common to the Chesapeake Bay.
Chemical contaminants
Pesticides, pharmaceuticals, metals and other toxic substances that can harm the health of both humans and wildlife.
Chlorophyll a
The predominant type of chlorophyll found in algae. Chlorophyll a is used as an indicator of nutrient pollution in the Bay and its tributaries.
Tiny, projecting "hairs" on a cell or microscopic organism that beat rhythmically to aid in movement.
Clean Water Act
Common name for the Federal Water Pollution Control Act. Its purpose is to "restore and maintain the chemical, physical and biological integrity of the nation's waters," whether on public or private land. It authorizes the U.S. Environmental Protection Agency (EPA) to set water quality criteria for states to use to establish water quality standards.
A group of eggs laid together at one time.
Coastal plain
The level land downstream of the piedmont and fall line, where soils are generally finer and fertile and rivers are influenced by the tide.
Coliform bacteria
A group of bacteria primarily found in human and animal intestines and wastes. Coliform bacteria (such as E. coli) are widely used as an indicator of the presence of such wastes in water.
A two-species association in which there is a positive effect on one species and neither a positive nor a negative effect on the other.
A group of organisms occurring together.
An interaction between members of two or more species that, as a consequence either of exploitation of a shared resource or of interference related to that resource, has a negative effect on fitness-related characteristics of at least one of the species.
Shaped like a cone.
Any needle-leaved or scale-leaved cone-bearing tree or shrub, such as pines, spruces and cypress.
The care and protection of natural resources.
Any organism that consumes other organisms (living or dead) to meet its energy needs.
Anything that makes the water or land impure, unclean or polluted.
Contaminants of emerging concern
Pharmaceuticals, personal care products and other chemicals that are being discovered in water that previously had not been detected or are being detected at levels that may be significantly different than expected. The risk to human health and the environment associated with the presence, frequency of occurrence or source of these contaminants may not be known.
Small, abundant planktonic crustaceans that are important food for fish.
Aquatic arthropods (invertebrates) that have gills, joined legs and exterior skeletons. Crabs, shrimps, barnacles, amphipods and isopods are all crustaceans.


Any barrier which impounds or diverts water.
A pesticide used widely in the mid-20th century to control mosquitoes. DDT was banned after it was found to cause bald eagles and other birds to lay eggs with brittle shells that would crack easily, causing populations to decline.
Dead zone
A condition where no oxygen is present in the water. Dead zones are often caused by the decomposition of algae blooms.
The process by which organic matter breaks down into simpler forms.
The removal of a forest, woodland or stand of trees without adequate replanting or natural regeneration.
Delmarva Peninsula
The land separating the Chesapeake Bay from the Atlantic Ocean. The Delmarva Peninsula falls within the states of Delaware (Del-), Maryland (-mar-) and Virginia (-va), from which it gets its name.
The loss or removal of nitrogen or nitrogen compounds.
An oyster disease caused by the protozoan parasite Perkinsus marinus, which many Chesapeake Bay oysters contract in their second year of life.
Designated use
The description of an appropriate intended use by humans and/or aquatic life for a water body. Designated uses for a water body may include recreation, shellfishing, water supply and/or aquatic life habitat.
Accumulated organic debris from dead organisms that is often an important source of food in a food web.
Any organism that gets most of its nutrients from the detritus in an ecosystem.
Microscopic algae with plate-like structures made of silica. Diatoms are considered a good food source for zooplankton.
A type of algae with long, whip-like structures called flagellates.
Dissolved inorganic nitrogen (DIN)
Nitrogen that is readily usable by plants.
Dissolved oxygen (DO)
The amount of oxygen that is present in the water. It is measured in units of milligrams per liter (mg/L), or the milligrams of oxygen dissolved in a liter of water. Just like humans, all of the Bay's living creatures need oxygen to survive.
An animal that is active during daylight.
An ecological measure of the variety of organisms present in a habitat.
Relating to or situated on an animal's back.
Drainage basin
An area of land that drains into a particular river, lake, bay or other body of water. We all live in a drainage basin: some are large (like the Chesapeake), while others are small (like your local stream or creek). Also called a watershed.
An apparatus used to bring up objects or mud from a river or seabed by scooping or dragging.
Dry deposition
Pollutants in the air that fall onto the land or water as dry particles, without the aid of precipitation.


A limited right to use a part of land owned by another person or organization.
Ebb tide
A falling tide.
A marine invertebrate animal that has tube feet and five-part radial symmetry. Sea stars and sea cucumbers are both echinoderms, which means "spiny-skinned."
The study of interrelationships between living things and their environment.
A natural unit formed by the interaction of a community of plants and animals with the environment in which they live. All of the elements of an ecosystem interact with each other in some way, depending on each other directly or indirectly.
Discharge of liquid waste from a wastewater treatment facility, factory or industry to a local waterbody.
Growing in water, with the majority extending above the water's surface.
Pollution released or discharged into the air from natural or man-made sources, including vehicles, smokestacks and the spraying of aerosols.
Endangered species
A species whose numbers are so small that it is in immediate danger of becoming extinct and needs protection to survive.
Endemic species
A species that is restricted in its distribution to a particular locality or region.
Endocrine disruptors
Synthetic chemicals that disrupt normal endocrine system functions in humans and wildlife by blocking or mimicing hormones. Known endocrine disruptors include PCBs, dioxins, DDT and some other pesticides.
Enhanced nutrient removal (ENR)
Wastewater treatment technology that improves upon the nutrient reductions achieved through biological nutrient removal (BNR).
The place in which an organism lives and the circumstances under which it lives. An environment includes measures like moisture and temperature as much as it refers to the actual physical place where an organism is found.
Environmental data
Any measurements or information that describe environmental processes, location or conditions; ecological or health effects and consequences; or the performance of environmental technology. For EPA, environmental data include information collected directly from measurements, produced from models and compiled from other sources such as databases or literature.
Environmental technology
An all-inclusive term used to describe pollution control devices and systems, waste treatment processes and storage facilities, and site remediation technologies and their components that may be utilized to remove pollutants or contaminants from the environment or prevent them from entering the environment.
Animals that live either attached to a hard surface (for example, on rocks or pilings) or move on the surface of bottom sediments. Epifauna include oysters, mussels, barnacles, snails, starfish, sponges and sea squirts.
A plant that grows upon another plant. The epiphyte does not "eat" the plant on which it grows, but uses the plant for structural support or as a way to get off the ground and into the canopy environment.
The disruption or movement of soil by wind, water or ice, occurring naturally or as a result of land use practices.
Estuarine species
A permanent resident of an estuary. Also called a resident species.
A partially enclosed body of water where fresh water from rivers and streams mixes with salt water from the ocean. It is an area of transition from land to sea.
Used to describe aquatic organisms that tolerate a wide range of salinities.
An aquatic system with high nutrient concentrations, which fuels algal growth. This algae eventually dies and decomposes in a process that reduces the amount of dissolved oxygen in the water.
The process of excess nutrients accelerating the growth of algae, ultimately depleting the water of dissolved oxygen.
Hard outer shell that provides an invertebrate with support and protection. Blue crabs and other crustaceans have exoskeletons.
Exotic species
Any introduced plant or animal species that is not native to a region. Exotic species are not always considered a nuisance or invasive.
Extant species
A species that is currently in existence (the opposite of extinct).
Extinct species
A species that has disappeared from existence due to either natural or human-induced means.


Fall line
The boundary between the Piedmont Plateau and the Coastal Plain, ranging from 15 to 90 miles west of the Bay. Waterfalls and rapids clearly mark this line, which is close to Interstate 195.
The rate at which an individual produces offspring, usually expressed only for females. For example, the number of eggs produced per female striped bass during a spawning season.
A natural substance or chemical added to soil or land to increase its fertility and help plants grow.
Filter feeder
An organism that feeds by straining plankton and other food particles from water that is pumped through its gills or mouth. For example, oysters and menhaden are filter feeders.
Fish ladder
A series of ascending pools of running water constructed to allow fish to swim upstream around or over a dam.
Fish passage
Features of a dam that enable fish to move around, through or over a dam without harm. Generally an upstream fish ladder or a downstream bypass system.
Fishing mortality rate
The percentage of fish removed from a species' population due to commercial fishing.
A long, threadlike or whip-like appendage found in certain cells or unicellular organisms that helps the cells move.
Flood tide
A rising tide.
Food chain/web
A food chain is formed as one organism eats another. A food web is a system of interlocking and interdependent food chains, in which each organism supplies energy to another life form.
Forest fragmentation
A form of habitat fragmentation occurring when large patches of forest are cut down in a manner that leaves smaller patches of trees standing. Forest fragmentation can be caused by wildfires or by the intentional clearing of trees to make room for roads and development, and can make it difficult for some species to breed or find food.
Forest parcelization
The division and sale of privately owned forestland into smaller pieces owned by more landowners.
Forest-interior species
Species that tend to avoid edge habitats and that require large tracts of forest habitat for nesting and foraging.
An increase of water flow into the Bay during late winter or spring due to increased precipitation and snow melt in the watershed.
Newly-hatched young fish.


The largest class of mollusks. Gastropods have a one-piece shell (univalve) or no shell at all, and travel by using a single large muscular foot. Snails and slugs are gastropods.
Geographic Information System (GIS)
A computer program used to view, store and analyze maps and other geographic information.
Water that is stored under the earth’s surface, in the cracks and spaces between particles of soil, sand and rock.


The natural home or environment in which a plant, animal or other organism lives, feeds and/or breeds.
Harmful algae bloom
An algae bloom that produces chemicals toxic to humans and aquatic life.
Streams at the source of a river.
Heavy metals
Any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations.
Plants without woody stems.
A substance that is toxic to plants and is used to destroy unwanted vegetation.
An animal that eats plants.
A plant or animal that has both male and female reproductive organs and secondary sexual characteristics.
Home range
An area to which an individual organism restricts most of its usual activities.
To crossbreed a plant or animal.
Hydric soil
Soil that is saturated or flooded with water for long enough during the growing season that its upper portion develops anaerobic or low-oxygen conditions.
The way water moves and is distributed via precipitation, runoff, storage and evaporation.
A plant that grows only in or on water or very moist soil.
A condition in which oxygen levels in water are very low.


Impaired waters
Waterways that do not meet state water quality standards. Under the Clean Water Act, section 303(d), states, territories and authorized tribes are required to develop prioritized lists of impaired waters.
A hardened surface or area that does not allow water to pass through. For example, roads, rooftops, driveways, sidewalks, pools, patios and parking lots are all impervious surfaces.
Indigenous species
A species that is native to the Chesapeake Bay region. It evolved on the North American continent and was present at the time of European colonization.
Animals and bacteria of any size that live in bottom sediments. Worms and clams are considered infauna. They form their own community structures within bottom sediments, connected to the water by tubes and tunnels.
The physical structures and facilities that support the functioning of a community, including roads, sewers, water lines and power supplies.
An animal that feeds on insects.
Integrated pest management (IPM)
A sustainable pest management approach that combines the use of biological, cultural, physical and chemical tactics to minimize economic, health and environmental risks.
Interior forest
Mature forest that is separate from other land uses and provides interior forest dwelling species with the moderate temperatures and light levels integral to their summertime habitat.
An animal (usually a fish) that displays both male and female characteristics. Intersex in fish has been linked to exposure to hormone-disrupting compounds such as pharmaceuticals, personal care products, herbicides, pesticides and agricultural products.
The area of shoreline between the high tide and low tide marks.
Introduced species
A species that has been intentionally or inadvertently brought into a region or area. Also called an exotic or non-native species.
An animal that lacks a backbone. Aquatic invertebrates include squids, shrimps, crabs, mollusks and sea stars.
A tiny, bug-like crustacean.


A wall or other barrier built out into a body of water to shelter a harbor, protect a shoreline from erosion and/or redirect water currents.
Any member of a species that is not yet sexually mature. Often used interchangeably with young of the year (YOY).


Keystone species
A species whose survival affects other organisms in an ecosystem. If a keystone species were removed from an ecosystem, the ecosystem would drastically change.


The span of time between the adoption of a pollution-reducing practice and the visible effects of that practice on a particular waterway.
Land cover
Anything that exists on and is visible from above the earth's surface. Examples include water, vegetation and exposed or barren land.
Land use
The way land is used by humans. Forest, agricultural land and urban/suburban land are all land uses.
The tiny, newly hatched stage of many insects and aquatic animals.
Light attenuation
Reduction in the amount of light that can penetrate through the water, usually caused by excess suspended sediment or algae blooms.
Littoral zone
The intertidal area of the shoreline, between the high tide and low tide marks.
The amount of a type of pollution that the Bay and its tributaries receive.
Low-impact development (LID)
Innovative stormwater management practices that mimic a site's pre-development hydrology. LID uses design techniques that reuse runoff and allow it to soak into the soil, helping to protect local water quality.


Large, generally soft-bodied organisms that lack backbones.
An individual alga large enough to be seen with the naked eye.
The region of Chesapeake Bay extending from the Susquehanna River to the mouth of the Bay, not including the tributaries.
Warm-blooded vertebrates that give birth to and nurse live young; have highly evolved skeletal structures; are covered with hair, either at maturity or at some stage of their embryonic development; and generally have two pairs of limbs, although some aquatic mammals have evolved without hind limbs.
Jaw-like organs on some invertebrates that are used for seizing and biting food.
A species that lives in the ocean.
A border habitat that connects shorelines to forests and wetlands. Marshes are found in fresh, brackish and salt water areas.
One of three pairs of claw-like structures located near the mouth on the heads of crustaceans.
A second larval form of the blue crab.
Moderately salty waters with salinities that range from 5 to 18 parts per thousand (ppt).
An aquatic system that is somewhere between eutrophic (nutrient enriched) and oligotrophic (nutrient poor).
An organism that can only be seen with a microscope.
A unit of measurement equal to one thousandth of a millimeter.
The seasonal movement of animals from one region to another.
A species that moves from one habitat or region to another on a regular or seasonal basis.
A phylum of invertebrates that includes bivalves (clams, oysters and mussels), gastropods (snails) and cephalopods (squids).
An animal’s shedding of its exoskeleton prior to new growth. For example, blue crabs and other crustaceans must molt—or shed their shells—in order to grow.
A single plant that has both male and female flowers.
A parasitic oyster disease that thrives in warm, high-salinity waters and can affect oysters of all ages.
An infectious disease that causes inflammation, tissue destruction and the formation of scar tissue in the organs of striped bass.


Native species
A species that is native to the Chesapeake Bay region. It evolved on the North American continent and was present at the time of European colonization.
Natural infrastructure
Natural physical systems that support life, such as water cycles, nitrogen cycles and water purification.
The relatively shallow waters between the shoreline and deeper, open waters.
A long, slender leaf found on loblolly pines and other evergreens.
Organisms that are able to swim through the water column and move against currents. Nekton include fish, blue crabs, whales and rays.
Stinging cells found on jellyfish and anemones. The "sting" is caused by a coiled, thread-like tube that is propelled outward for defense and to capture food.
When a bird makes, repairs or lives in a nest in preparation for giving birth to young.
The particular area within a habitat that an organism lives and functions in.
The process by which ammonia is oxidized into nitric acid or another nitrate or nitrite. Biological nitrification is a key step in the removal of nitrogen from wastewater.
A type of nutrient that contributes to the Bay's poor water quality. While nitrogen is needed for plant growth, human activities--like driving cars or applying fertilizers--contribute more nitrogen than the Bay's waters can handle. Elevated nitrogen levels cause more algae to grow, blocking out sunlight and reducing oxygen for fish, crabs and other Bay life.
An animal that is only active at night.
Non-point source
A source of pollution that cannot be attributed to a clearly identifiable, specific physical location or a defined discharge channel. Non-point source pollution includes nutrients that run off croplands, feedlots, lawns, parking lots, streets and other land uses. It also includes nutrients that enter waterways via air pollution, groundwater or septic systems.
A flexible, primitive backbone that forms the main body support of sea squirt larvae and some other marine animals.
Nutrient removal technology (NRT)
Technology that removes nitrogen and phosphorus during wastewater treatment. Also known as biological nutrient removal (BNR).
Nutrient trading
The transfer of nutrient reduction credits, specifically for nitrogen and phosphorus.
Chemicals that plants and animals need to grow and survive but, in excess amounts, can harm aquatic environments. Elevated levels of the nutrients nitrogen and phosphorous are the main cause of poor water quality in the Chesapeake Bay.


Brackish waters with low salinities that range from 0.5 to 5 parts per thousand (ppt).
A water body or habitat with low concentrations of nutrients.
An organism that will eat both plants and animals.
Open space
An area of land that is valued for natural processes and wildlife, agricultural and sylvan production, active and passive recreation and/or other public benefits.
To remain alive or viable throughout the winter.


Sensory appendages located near the mouth on many invertebrates that are used to move and sense food.
Paired appendages or feet found on each segment of bristle worms and other segmented marine worms.
A plant or animal that lives on or in another species and derives its nutrition and/or protection, often with harmful effects to the host.
A bacterium, virus or other microorganism that can cause disease.
The open ocean, excluding the ocean bottom and shore.
Plants that live for more than two growing seasons. Perennial plants either die back after each season (herbaceous plants) or grow continuously (shrubs).
Having pores or openings that allow water to pass through.
A porous surface that water is able to penetrate through.
A general term that describes the chemical substances used to destroy or control insect or plant pests. Many pesticides are manufactured and do not occur naturally in the environment. Others are natural toxins that are extracted from plants and animals.
A measure of the acidity or alkalinity of water.
Compounds manufactured for use as medicinal drugs.
A type of nutrient contributing to the Bay's poor water quality. While phosphorus is vital to plant life, human activities--like applying fertilizers or using household cleaners--contribute more phosphorus than the Bay's waters can handle. Elevated phosphorus levels cause more algae to grow, blocking out sunlight and reducing oxygen for fish, crabs and other Bay life.
Photic zone
The layer of water that sunlight is able to penetrate through and reach plants growing underwater.
The process by which plants convert carbon dioxide and water into carbohydrates and oxygen. These carbohydrates are used as energy by the plants or by organisms that consume the plants. Photosynthesis is also called primary production.
Tiny, single-celled planktonic plants. Also called algae. Phytoplankton are the primary producers of food and oxygen in the Bay food web.
Uplands or hill country located above the fall line. Rivers and streams in the Piedmont region are not influenced by the tide.
A fish-eating animal.
Small and microscopic free-floating plants, animals and bacteria. Plankton have limited or no swimming ability and are transported by currents and tides.
The lower part of a turtle's shell.
The feathers that cover a bird's body.
Point source
A source of pollution that can be attributed to a specific physical location - an identifiable, end-of-pipe "point." The vast majority of point source discharges of nutrients are from wastewater treatment plants, although some come from industries.
To fertilize a plant by transferring pollen grains from a male plant structure to a female plant structure.
The introduction of harmful substances or products into the environment.
Polychlorinated biphenyls (PCBs)
A chemical contaminant that was once used as a flame retardant in electrical equipment. Though their production has been banned since 1977, PCBs persist in the environment, posing a risk to humans and wildlife.
Polycyclic Aromatic Hydrocarbons (PAHs)
A chemical contaminant that forms when gas, coal and oil are burned. PAHs are common in areas with high rates of development and motor vehicle traffic.
Salty waters with salinities that range from 18 to 30 parts per thousand (ppt).
All persons present in a particular area.
A measurement of water salinity; stands for "parts per thousand."
Rain, snow, sleet or hail that falls to the ground.
The preying of one animal on others.
An animal that hunts for and eats other plants or animals.
A plant or animal that is hunted for and eaten by a predator.
Primary producers
Organisms, such as algae, that convert solar energy to organic substances through chlorophyll. Primary producers serve as a food source for higher organisms.
Probable Effects Level (PEL)
An estimate of the concentration of a potentially toxic substance in sediment, above which the toxic substance is likely to cause adverse effects in aquatic organisms.
A long or tubular mouth part in certain insects, worms and spiders that is used for feeding, sucking and other purposes.
The zone or boundary where the fresher water layer on the surface meets the saltier water layer below. The pycnocline can be a physical barrier that prevents mixing or exchange between the two layers.


Quality Assurance (QA)
An integrated system of management activities involving planning, implementation, documentation, assessment, reporting and quality improvement to ensure that a process, item or service is of the type and quality needed and expected by the customer.
Quality Assurance Project Plan
A document describing in comprehensive detail the necessary quality assurance, quality control and other technical activities that must be implemented to ensure that the results of the work performed will satisfy the stated performance criteria.
Quality Control (QC)
The overall system of technical activities that measures the attributes and performance of a process, item or service against defined standards to verify that they meet the stated requirements established by the customer; operational techniques and activities that are used to fulfill requirements for quality.
Quality Management
That aspect of the overall management system of the organization that determines and implements the quality policy. Quality management includes strategic planning, allocation of resources and other systematic activities (e.g., planning, implementation, documentation and assessment) pertaining to the quality system.
Quality Management Plan
A document that describes a quality system in terms of the organizational structure, policy and procedures, functional responsibilities of management and staff, lines of authority, and required interfaces for those planning, implementing, documenting and assessing all activities conducted.
Quality System
A structured and documented management system describing the policies, objectives, principles, organizational authority, responsibilities, accountability and implementation plan of an organization for ensuring quality in its work processes, products (items) and services. The quality system provides the framework for planning, implementing, documenting and assessing work performed by the organization and for carrying out required quality assurance and quality control.


Body parts on an invertebrate that are arranged in a circle around a single center.
A flexible, toothed organ in the mouths of gastropods used to graze and scrape microscopic algae off hard surfaces.
Rain garden
A garden that uses plants and layers of soil, sand and mulch to retain rainwater, reducing the amount of polluted runoff that reaches storm drains and local waterways.
The geographic area in which a plant or animal lives.
A bird of prey, including eagles, ospreys and hawks.
The addition of new individuals to a population by reproduction, commonly measured as the proportion of young in the population just before the breeding season.
Red tide
A dense outburst of dinoflagellates that colors the water reddish-brown. Certain dinoflagellates can produce toxins that kill fish and contaminate shellfish.
The natural or intentional restoration of a forest, woodland or stand of trees that had been lost due to fire, cutting or other method of deforestation.
A natural or artificial place where water is collected or stored for use, especially water for supplying a community, irrigating land and furnishing power.
A species that lives permanently in a particular area.
The underground portion of a plant's stem. Rhizomes are usually thick and horizontal, produce roots and have shoots that develop into new plants.
The area of land next to a body of water. Riparian areas form the transition between terrestrial and aquatic environments.
Riparian forest buffers
Trees, shrubs and other vegetation located along the edge of rivers, streams and other waterways that filter pollution, prevent erosion and provide wildlife habitat.
Of a river, relating to or produced by a river.
The eggs or egg mass of a fish.
The underground portion of a plant's stem, also called a rhizome.


A measure of the salt concentration of water. Higher salinity means the water is more salty, while low salinity means that the water is more fresh. Salinity is usually measured in parts per thousand (ppt).
Salinity regime
Water distinguished by its salinity and tidal influence. The major salinity regimes are tidal fresh, oligohaline (brackish), mesohaline (moderately salty) and polyhaline (salty).
Salt marsh
Wetlands that are located in salt water areas and are dominated by cordgrass, also called Spartina. Salt marshes are one of the most productive plant communities on earth.
An opportunistic animal that feeds on decaying plants and animals or scraps of food abandoned by other animals.
Large, bony plates covering animals such as sturgeon, turtles and sticklebacks.
Loose particles of sand, silt and clay that settle on the bottom of rivers, lakes, estuaries and oceans. Suspended sediment pushed into the water by erosion is one of the biggest impairments to water quality in the Chesapeake Bay.
The accumulation of sediment in an area, filling shipping channels and covering oysters and other bottom-dwelling organisms. Sedimentation is also called siltation.
An organism that is immobile because it is attached to a hard surface, such as oysters, sea squirts and barnacles.
Aquatic animals, such as clams, crabs, oysters and shrimps, that have a shell or shell-like external skeleton.
The process by which sediment is suspended and deposited in a body of water. Also referred to as sedimentation.
Ozone, particulate matter, humidity and other pollutants that mix together in the air and reduce visibility.
Juvenile oysters that have just attached to a hard surface.
To release eggs and/or sperm into the water.
A group of organisms made up of similar individuals that are capable of breeding with one another.
Small, needle-like projections that make up the skeleton of a sponge.
Land development that is built away from urban areas and existing town centers, creating large areas of relatively low-density residential and commercial development.
The male reproductive organ of a flower.
Adding fish to a body of water, such as a lake, pond or stream.
Any precipitation in an urban or suburban area that does not evaporate or soak into the ground, but instead collects and flows into storm drains, rivers and streams. Stormwater is also called urban stormwater, stormwater runoff and polluted runoff. Increased development across the Chesapeake Bay watershed has made stormwater the fastest growing source of pollution to the Bay and its rivers and streams.
The division of warmer, lighter fresh water over a layer of saltier and denser water in the Bay. Stratification of the two layers varies within any season depending on rainfall.
Stream bank erosion
Loss of sediment along a stream bank as a result of increased runoff from nearby development. Stream bank erosion degrades stream habitats for wildlife and increases suspended sediments in the water.
Submerged aquatic vegetation (SAV)
The technical term for bay grasses that grow underwater. SAV can improve water quality and provide food and habitat to fish, shellfish and waterfowl.
The surface or material that an organism lives on or in. For example, oyster reefs provide hard substrate for invertebrates to attach themselves to.
The area of shoreline that is always submerged, even at the lowest tide.
The process by which a plant or animal community successively gives way to another until a stable state is reached.
Suspended sediments
Tiny particles of clay and silt that become suspended in the water, reducing water clarity and the amount of sunlight that can reach underwater bay grasses. Excess suspended sediment is one of the largest contributors to the Bay's impaired water quality.
Maintaining an ecological balance by avoiding depletion of natural resources.
A type of wetland dominated by woody vegetation or trees.
Swim bladder
A gas-filled organ that regulates buoyancy in most bony fishes.


An organism that lives on the land.
A thick, tangled growth of shrubs, bushes and/or small trees.
A species that is likely to become endangered if not protected.
Tidal marsh
A type of marsh in which the flooding characteristics are determined by the tidal movement of the adjacent river, estuary, sea or ocean.
Tidal mud flat
The unvegetated area of shore that is exposed during low tide.
The alternate rising and falling of the sea caused by the gravitational attraction of the earth, sun and moon.
Total maximum daily load (TMDL)
Defines the pollutant load that a water body can acquire without violating water quality standards, and allocates the pollutant loading between contributing point sources and non-point sources.
A toxic agent that is harmful to plants and animals.
Trend analysis
A formal statistical process used to determine the presence or absence of changes in measures of water quality over time or a geographic area.
A creek, stream or river that flows into a larger body of water. For example, the Susquehanna, Potomac and James rivers are tributaries of the Chesapeake Bay.
Tributary strategies
River-specific cleanup plans that detail the actions needed to achieve nutrient and sediment cap load allocations that are developed in cooperation with local watershed stakeholders.
Trophic level
Each step along a food chain; an organism's feeding level.
The thickness, opaqueness or reduced clarity of water caused by the suspension of sediments. The turbidity of rivers and streams increases after a rainfall.


The layer of forest located underneath the canopy. Here, smaller trees and shrubs grow, replacing older trees as they die.
Urban forest
The system of trees and associated plants that grow in small groups or under forest conditions on public and private lands in cities, suburbs and towns. This includes the approximately 74.4 billion trees in the U.S. that are located in parks, along streets and around private homes and businesses.
The process by which an area of land becomes more urban in character, developed and otherwise changed to more closely resemble a city or town.
Use attainability analysis (UAA)
A structured scientific assessment of the factors affecting attainment of the designated use component of water quality standards, based on physical, chemical, biological and/or economic factors.


A shell on a mollusk. Mollusks with two shells (such as clams and oysters) are called bivalves.
Free-floating, planktonic larvae of certain mollusks, such as snails, oysters and sea slugs.
A poisonous fluid produced by an animal that is transmitted by a bite or a sting. Venom is used to capture prey or as a means of defense.
An animal with a backbone, including fish, amphibians, reptiles, birds and mammals.


Water that has been used in homes, industries and businesses that is not reuseable unless treated by a wastewater treatment facility.
Water clarity
A measure of the amount of sunlight that can penetrate through the water.
Water quality criteria
Water quality conditions necessary to protect aquatic plants and animals.
Water quality standards
Standards that define the goals for a water body by designating its uses, setting criteria to protect those uses, and establishing provisions to protect water bodies from pollutants.
Any of various birds that swim on water or rely on aquatic environments, including ducks, geese and swans.
An area of land that drains into a particular river, lake, bay or other body of water. We all live in a watershed: some are large (like the Chesapeake), while others are small (like your local creek, stream or river).
Wet deposition
Pollutants in the air that fall onto the land or water with rain or snow.
A transitional zone between land and water that is periodically flooded. For example, marshes, swamps and bogs are all wetlands.


Year class
All of the fish of any species that hatched during one annual spawning period.
Young of the year (YOY)
All of the fish of a species that were born in the past year, from transformation to juvenile until January 1.


A tiny, semi-transparent larval blue crab.
Planktonic animals that float in the water and range in size from single-celled protozoa to comb jellies. Zooplankton feed on detritus, phytoplankton and other zooplankton. They are eaten by fish, shellfish and whales.