Record rainfall in 2018 had complex effects on the health of Baltimore waterways

Mention Baltimore, and after blue crabs, Old Bay and the Orioles, most people will think of the iconic Inner Harbor. Once a bustling seaport, it is now known mainly as a tourist destination, as home to the world-renowned National Aquarium and sadly, as often being filled with trash and sewage.

Several organizations throughout the city and state are committed to improving Baltimore’s waterways. One of these organizations, Blue Water Baltimore, recently released their annual report on the water quality of the Inner Harbor and its tributaries.

Most of the Chesapeake Bay watershed experienced the wettest year on record in 2018, and Baltimore was no exception, with 71 inches of rain reported. Blue Water Baltimore samples water quality at 49 monitoring stations throughout this region year-round, following the process outlined in the Maryland Tributary Assessment. In 2018, water quality within this region fell within the very poor (zero to 59 percent) or poor (60 to 69 percent) categories.

The Gwynns Falls watershed saw significantly worse turbidity (how clouded with sediment the water can be) and phosphorus scores than ever before, most likely due to the record rainfall and associated runoff. Normally, an increase in phosphorus would lead to a rise in algae blooms in the Inner Harbor and tidal Patapsco River, but the rains essentially flushed it out to the Bay before it could grow into a bloom. This led to record low chlorophyll-a levels throughout the tidal waterways, which is a measure of algae. Furthermore, despite the rainfall, bacteria scores in non-tidal waterways continued to improve, which may be a result of updates to pipe infrastructure.

Gwynns Run, a tributary of Gwynns Falls located in southwest Baltimore, recorded the lowest water quality of the region at 35 percent, thanks in large part to the number of fecal bacteria found in the samples taken.

Stoney Creek, a tributary of the Patapsco River, and Dead Run, a tributary of Gwynns Falls located in west Baltimore, recorded the best water quality scores of the region at 62 percent, thanks in large part to high amounts of dissolved oxygen. Dissolved oxygen is vital for the health of fish, shellfish and other aquatic species, as it allows them to breathe in the water. When dissolved oxygen levels are low, nutrient-rich algae can form what is commonly referred to as a “dead zone.”

More detailed information about each monitoring station is available on Blue Water Baltimore’s new water quality mapping tool: Baltimore Water Watch.