Chesapeake Bay sees slight improvement in water quality

Annapolis, MD—The Chesapeake Bay Program announced today that an estimated 29.8% of the Chesapeake Bay and its tidal tributaries met water quality standards for clarity (measured by underwater grass abundance), dissolved oxygen and chlorophyll a (a measure of algae growth) during the 2020-2022 assessment period. This is a slight improvement from the 28.1% estimated during the previous assessment period of 2019-2021. Water quality in the Chesapeake remains below the 100% attainment necessary to support a healthy Bay ecosystem.

The slight increase in Bay water quality noted in the most recent assessment period of 2020-2022 is due to higher levels of dissolved oxygen in the deep waters of the Chesapeake (which can lead to a smaller dead zone), while clarity in the shallow waters of the Bay remained poor due to a lower acreage of underwater grasses (Note: The Chesapeake Bay Program released the most recent estimate of underwater grass acreage in July 2024 which will be accounted for in next year’s assessment of water quality standards attainment).

In addition to the three monitoring parameters mentioned above, water quality in the Chesapeake Bay and its tidal tributaries is also influenced by nitrogen, phosphorus and sediment trends from across the watershed. And for the first time, Bay Program experts are using a new indicator referred to as the Chesapeake Bay Total Maximum Daily Load Indicator, or Bay TMDL Indicator, that combines both monitoring and modeling data to better understand how the Chesapeake Bay is responding to installed best management practices and other watershed changes, while accounting for climate change impacts and lag times, among other factors.

The seven watershed jurisdictions–Delaware, District of Columbia, Maryland, New York, Pennsylvania, Virginia and West Virginia–work with local governments, businesses, non-profit organizations, farmers and individuals to install best management practices to lower the amount of nitrogen, phosphorus and sediment pollution that enters local waterways and the Chesapeake Bay. Management actions taken to decrease pollution from point sources (e.g., wastewater treatment plants) may immediately show detectable pollution changes, but the implementation of best management practices for non-point sources often shows a lag time in measuring their impact on improving water quality and the health of the Bay.

Bay TMDL Indicator

For the Chesapeake Bay and its tidal tributaries to function as a healthy ecosystem and meet applicable water quality standards, annual nitrogen and phosphorus pollution entering the Bay must be 145.24 and 9.33 million pounds lower, respectively, than the 1995 baseline. The period 1993-1995 was chosen to determine the overall effort required to meet the Chesapeake Bay Total Maximum Daily Load, accounting for the amount of nitrogen and phosphorus pollution entering the Bay at that time.

Impacts from climate change, infill from the Conowingo Dam reservoir and a variety of other factors during the period 1995-2022 have added approximately 10.49 million pounds of nitrogen and 0.8 million pounds of phosphorus to the original targets for pollutant reductions called for in the Chesapeake Bay Total Maximum Daily Load.

Bay Program experts estimate that between 1995 and 2022, 80.95 million pounds of nitrogen and 2.4 million pounds of phosphorus were reduced through the installation of best management practices. It is believed that an additional approximately 4.72 million pounds of nitrogen and 1.74 million pounds of phosphorus will be reduced annually as a result of the installed best management practices, but these declines have not yet occurred due to a natural lag time.

“We now have new tools to help us evaluate and visualize our progress toward meeting pollutant reduction goals,” said Bryant Thomas, manager of the Office of Ecology at the Virginia Department of Environmental Quality and vice-chair of the Chesapeake Bay Program Water Quality Goal Implementation Team. “The Bay Total Maximum Daily Load Indicator and the Monitored and Expected Total Reduction Indicator for the Chesapeake are great advancements that help all partners be more strategic in their clean-up efforts.”

Tidal and Nontidal Water Quality

The U.S. Geological Survey works with partners from D.C. and the watershed states to monitor nitrogen, phosphorus and sediment pollution entering the Chesapeake Bay from its 64,000-square-mile watershed. Stream flow and water quality conditions have been measured at River Input Monitoring (RIM) stations located on the nine largest tributaries of the Bay since 1985. Over time, the monitoring network has expanded to more than 100 non-tidal stations across the region.

Pollution amounts vary from year to year due to a number of factors, including land use, fertilizer and manure use, wastewater and septic discharges, and river flow. Monitoring data from the nine RIM stations represent the amount of nitrogen, phosphorus and sediment that is entering the Chesapeake from 78% of its watershed, while the remaining 22% of pollution entering the Bay is estimated through combining data from wastewater treatment plants and computer-simulated estimates of nitrogen and phosphorus pollution from nonpoint sources.

River Flow, Pollution Loads and Trends

In 2022, average river flow to the Bay measured 47.2 billion gallons per day, a decrease of 7.6 billion gallons per day from the previous year, bringing 253 million pounds of nitrogen, 13.4 million pounds of phosphorus and 14.2 billion pounds of sediment into the Chesapeake. These are decreases from the previous year (2021) of 11.5%, 33% and 20%, respectively.

The U.S. Geological Survey assesses trends in nitrogen, phosphorus and sediment pollution entering the Bay from the nine RIM stations to produce short-term trends. The most recent short-term trends, from 2013-2022, show a mix of improving and degrading conditions throughout the watershed.

• Trends in nitrogen indicate improving conditions at four stations (James, Patuxent, Potomac, Susquehanna), degrading conditions at four stations (Appomattox, Choptank, Mattaponi, Rappahannock) and no trend at the Pamunkey station.

• Trends in phosphorus indicate improving conditions at three stations (Patuxent, Potomac, Susquehanna), degrading conditions at three stations (Appomattox, Choptank, Rappahannock) and no trend at the James, Mattaponi and Pamunkey stations.

• Trends in sediment indicate improving conditions at three stations (Pamunkey, Patuxent, Susquehanna), degrading conditions at four stations (Appomattox, Choptank, Mattaponi, Rappahannock) and no trend at the James and Potomac stations.

The U.S. Geological Survey also analyzes short-term trends in nitrogen, phosphorus and sediment pollution at the non-tidal stations throughout the watershed. The following are the most recent short-term trends, from 2011-2020.

• Thirty-eight percent of 89 non-tidal network stations showed an improvement in the amount of nitrogen pollution, whereas 42% were degrading and 20% showed no change.

• Forty-four percent of 70 non-tidal network stations showed an improvement in the amount of phosphorus pollution, whereas 23% were degrading and 33% showed no change.

• Eighteen percent of 70 non-tidal network stations showed an improvement in the amount of sediment pollution, whereas 46% were degrading and 36% showed no change.

“The River Input Monitoring stations and non-tidal monitoring network are critical to the partnership for documenting how water quality conditions are changing across the watershed,” said Ken Hyer, Chesapeake Bay coordinator with the U.S. Geological Survey. “While the results show progress in many rivers, they also highlight that the partnership has more work ahead of it.”

Excess nitrogen, phosphorus and sediment are among the leading causes of the Chesapeake Bay’s poor health. Nitrogen and phosphorus can fuel the growth of algae blooms that lead to low-oxygen dead zones. These conditions can suffocate plant and animal life, reducing the habitat available to them. Sediment can block sunlight from reaching underwater grasses and bury shellfish. But by measuring the achievement of water quality standards, experts can observe crucial changes in the Bay’s health over time and gain a better picture of how pollution from the watershed is impacting the health of the Chesapeake.

“Thanks to the collaborative efforts of our many partners, the Chesapeake Bay Program continues to refine our data-driven water quality indicators, allowing us to gain a better understanding of the Chesapeake’s complex health,” said Martha Shimkin, director of the Environmental Protection Agency’s Chesapeake Bay Program Office. “While some areas of the watershed are showing recent gains in water quality, others are displaying less than ideal conditions. As the partnership is hard at work in determining the next phase of Bay restoration beyond 2025, tidal and non-tidal water quality monitoring and modeling will continue to serve as a foundation for our conservation- and restoration-driven work.”