Monitoring the Chesapeake Bay and its tributaries allows Bay Program partners to detect changes that take place in the ecosystem, reveals trends over time that can provide valuable information to policy makers and improves our understanding of the natural world. The Chesapeake Bay Monitoring Program, which began in 1984, is a Bay-wide cooperative effort involving watershed jurisdictions, several federal agencies, 10 institutions and over 30 scientists.

What do Bay Program partners monitor?

Nineteen physical, chemical and biological characteristics are monitored 20 times a year in the Bay's mainstem and many tributaries.

Freshwater Inputs

Freshwater flowing into the Bay is monitored through an extensive network of monitoring stations. Freshwater inputs influence Bay salinity, nutrient loads, dissolved oxygen levels and other water quality parameters, as well as indirectly affect fish and shellfish populations.

Nutrients and Sediment

Nitrogen, phosphorus and suspended sediment are monitored through a tidal and non-tidal network of monitoring stations. Nutrients contribute to excessive algae growth and decomposition, which can deplete dissolved oxygen that aquatic life needs to survive. Sediment suspended in the water column blocks light underwater grasses need to grow.

Chemical Contaminants

Chemical contaminants—both organic compounds and heavy metals—enter the Bay from a variety of sources, including wastewater, industries, atmospheric deposition and runoff from agricultural, urban and suburban land. These contaminants have been found in sediments at high levels, as well as in the tissues of animals like birds and fish.


In cooperation with the U.S. EPA, the Bay Program has monitored phytoplankton and primary production in the Bay and its tributaries since August 1984. This series of monitoring programs give comprehensive spatial and temporal information on the plankton community. Sampling parameters include detailed taxonomic identifications and abundance measurements of target trophic groups, and geometric shapes of various plankton taxon may be used in calculations to determine carbon sequestration in the Bay.


Maryland and Virginia, in cooperation with the Bay Program, have monitored benthic species abundance in the Bay mainstem and tributaries since the mid-1980s. Benthos monitoring is designed to give comprehensive spatial and temporal information on benthic conditions in the Bay. Data collected as part of this program include detailed taxonomic identifications and counts of benthic species, determination of sample biomass, sediment analysis and hydrographic profiles.

In 1996, a Benthic Sediment Profile Images (SPI) and Image Analysis component was added to Virginia's monitoring program. SPI data are composed of photographic images and image analysis of the vertical bottom sediment profiles.

Finfish and Shellfish

Finfish and shellfish, including anadromous fish, marine-spawning fish, blue crabs and other shellfish, are monitored through stock assessments, fish lift usage and various habitat monitoring initiatives, such as water quality surveys and bottom-mapping.

Submerged Aquatic Vegetation (SAV)

Submerged Aquatic Vegetation—also known as underwater grasses—are a significance source of food for waterfowl and habitat for blue crabs and juvenile finfish. The steep decline in underwater grasses since the 1960s is believed to be the result of human activity. Chesapeake Bay SAV data consist of aerial photography from 1971; 1974; 1978; 1979 (Maryland only); 1980 and 1981 (Virginia only); 1984 through 1987; and 1989 through 1999. The most current data are available through the Virginia Institute of Marine Science.

Learn more about our approach to monitoring SAV

Water Temperature, Salinity and Dissolved Oxygen

The Bay Program provides funding to Maryland and Virginia to routinely monitor 19 directly-measured water quality parameters at 49 stations in the Bay's mainstem. The Water Quality Monitoring Program began in June 1984, with stations sampled twice each month in June, July and August and once each month the rest of the year. Special sampling events—called cruises—may be added to record unique weather events.

Organizations coordinate the sampling times of their respective stations so that data for each cruise represents a synoptic picture of the Bay at that point in time. At each station, a hydrographic profile—including water temperature, salinity and dissolved oxygen—is made at approximately 1- to 2-meter intervals. Water samples for chemical analysis, such as nutrients and chlorophyll, are collected at the surface and bottom, and at two additional depths depending on the existence and location of a pycnocline. Correlative data on sea state and climate are also collected.

Monitoring resources

  • The EPA publishes Multi-Resolution Land Characteristics (MRLC) Land Cover data on 15 classes of land cover—water, low-intensity developed high-intensity residential, high-intensity commercial/industrial, hay/pasture, row crops, other grass, evergreen forest, mixed forest, deciduous forest, woody wetland, emergent herbaceous wetland, and three classes of bare.
  • NASA LANDSAT Imagery gathers remotely sensed images of the land surface and surrounding coastal regions for global change research, regional environmental change studies and other civil and commercial purposes.
  • National Wetlands Inventory (NWI) data is published by the U.S. Fish and Wildlife Service. Each data layer comprises the area equivalent to one 7.5' quad (1:24,000 scale) map. Wetlands are delineated from photo interpretation of aerial photography, mapped on stable-base copies of 7.5' quad sheet overlays and either manually digitized or scanned. Within the Chesapeake watershed there are 1,336 7.5' quads wholly or partially contained.
  • The EPA's Environmental Monitoring and Assessment Program provides both point data sets and GIS databases for its study areas, including the Chesapeake Bay region (the Virginian province) and the rest of North America.