Recent Progress: Mixed

Analysis of tidal and nontidal water quality monitoring data are showing mixed results across the suite of key indicators that assess whether our management actions are having the expected reduction in pollutant loads and corresponding improvements in water quality. Funding has been identified that will begin to address long-term funding shortfalls for the water quality monitoring program; however, additional funding is needed. Annual reporting is on course and increasing with new reports and scientific journal publications focused on bay health improvements and watershed factors affecting trends in nutrient and sediment pollution.

Outlook: Off Course

Although progress is being made in reducing nutrients in the bay and bay response shows declines in the duration of annual hypoxia, only about 30% of the tidal waters are estimated to have attained water quality standards for dissolved oxygen, water clarity/SAV and chlorophyll a during the 2018-2020 assessment period. With less than 50% of the 123 nontidal monitoring sites showing improvement for nitrogen and phosphorus for trends between 2011-2020, watershed results are also considered off course. During 2021 and 2022, the Chesapeake Bay Program conducted a monitoring program review and presented recommendations to the Principals’ Staff Committee with funding targets that would sustain and enhance existing core networks. New partners and additional funding support are needed to address shortfalls and fulfill decision-support expectations of the Partnership.


Four indicators are used to measure progress toward the Water Quality Standards & Attainment Outcome: the extent of water quality standards achievement, changes in annual pollution loads and river flow, trends in pollution loads to major rivers entering the Bay, and trends in pollution loads in the watershed.

Water Quality Standards Achievement: Decline

An estimated 29.6% of the Chesapeake Bay and its tidal tributaries met water quality standards during the 2018-2020 assessment period. The effects on water quality resulting from high nutrient and sediment loads delivered to the bay during two recent above average flow years (2018 – 2019) have impacted the results. This score is lower than the previous score of 33.1% received during the 2017-2019 assessment period and shows a continued decline in the assessment status since the record high of 42.2% was achieved during the 2015-2017 assessment period.

Periods of improvement and decline in the combined measure of water quality correlate with significant changes in rainfall patterns across the region, the resulting nutrient and sediment loads delivered to the bay, and algal blooms that lead to poor water clarity and low dissolved oxygen in bay habitats. Experts attribute the recent ongoing decline in the assessment status of the overall indicator for the period 2018-2020 to the impacts on water quality resulting from unusually wet weather. Higher than average river flows entering the bay delivered abundant pollutant loads in 2018 and 2019 (see next flow and pollutant chart).

The indicator score combines evaluations of dissolved oxygen conditions, water clarity with submerged aquatic vegetation and chlorophyll a measures. Looking at the individual parameter assessments for 2018-2020, there were declines in the chlorophyll a attainment assessment – a signal of more algae in the water. Dissolved oxygen standards attainment also declined in key habitats. However, despite the record high river flows to the Bay in 2019, the 2018-2020 period of assessment saw significant improvements in the attainment for water clarity and submerged aquatic vegetation, representing shallow water conditions, and dissolved oxygen in deep water habitat. Indications of improvement during the stress of high flow impacts to Chesapeake Bay habitats may reflect increasing resilience in the Bay ecosystem over the long term. Nonetheless, the estimated water quality standards attainment of 29.6% for 2018-2020 remains far below the 100% attainment necessary to fully support survival, growth and reproduction of its living resources. If the Bay and its tidal tributaries are to function as a healthy ecosystem and be taken off of the impaired waters listings under Section 303(d) of the Clean Water Act, all applicable water quality criteria must be met simultaneously as defined in the water quality standards of Maryland, Virginia, Delaware and Washington D.C.

Annual Pollution Loads and River Flow to the Bay: Improvement

During 2020, average river flow to the Bay measured 50.3 billion gallons per day, a 40% reduction from the previous year, which, at 83.7 billion gallons per day, was a record river flow to the Bay since measurements began in 1937. The corresponding pollutant loads entering the Bay in 2020 were approximately 246 million pounds of nitrogen, 14.4 million pounds of phosphorus, and 14.9 billion pounds of sediment, a reduction of 49%, 47%, and 34% from the previous year, respectively.

Bay water quality is influenced by a variety of factors including nutrient and sediment loads delivered from the watershed into the bay. Nutrient and sediment loads are influenced by land use, land management, and river flow. Generally, when the watershed receives more rain and river flows increase, the water carries more sediment and nutrient pollution than usual. As described previously, the high flows and pollutant loads to the Bay in 2018 and 2019 contributed to the worsening of attainment of standards during the most recent reporting periods. The experts attribute reductions in nitrogen, phosphorus, and sediment loads during 2020 primarily related to a smaller river flow, but they also suggest the decline in phosphorus and sediment could be a result of management actions toward controlling point and nonpoint source pollution in the Bay watershed.

The source of the information of loads and river flow to the Bay include the loads from the River Input Monitoring (RIM) stations, point source discharges into tidal waters, and an estimate of nonpoint source below the RIM stations from the Chesapeake Bay Program’s Watershed Model, CAST-2019.

Trends in the Major Rivers Entering the Bay: Mixed

The nutrient and sediment load trends of the nine major rivers entering the Bay, known as the River Input Monitoring (RIM) stations, are updated every year. Together, these stations reflect the nutrient and sediment loads delivered to the Bay from nine major tributaries representing 78% of its watershed and contribute to the annual pollution load impacting bay health and the Bay indicator results.

In July 2021, the USGS released its analysis of the long-term (1985 to 2020) and ten-year (2011 to 2020) trends in nutrient and sediment loads at nine River Input Monitoring (RIM) stations. These nutrient and sediment load trends are summarized in the table below. The trend qualifiers “improving,” “degrading,” and “no trend” are based on Chesapeake Bay restoration goals for water quality attainment (reduction of nutrients and sediments) in the Bay. “No trend” indicates that an “improving” or “degrading” trend is about as likely to exist as it is not, based on the trend estimation approach.

Pollution Loads by Monitoring Station

While the table describes the short-term and long-term trends at each monitoring station individually, in summary, over the long term, trends in nitrogen have improved at six stations including the four largest rivers (Susquehanna, Potomac, James, and Rappahannock), along with the Patuxent and Mattaponi, degraded at two stations (Choptank and Appomattox) and showed no discernable trend at one station (Pamunkey). Phosphorus loads showed long-term improvements at four stations (Susquehanna, Patuxent, Potomac, and James), degrading conditions at four stations (Choptank, Rappahannock, Pamunkey, and Appomattox), and no discernable trend at one station (Mattaponi). Sediment loads improved at three stations and (Choptank, Patuxent, and Potomac), degraded at five stations (Susquehanna, Rappahannock, Pamunkey, James, and Appomattox), and showed no discernable trend at one station (Mattaponi).

Trends in Loads in the Watershed: Mixed

Nutrient and sediment load trends are computed for the 123 nontidal network sites every other year. For nitrogen, results between 2011-2020 showed 37% of the 123 sites had improving trends but 40% had degrading trends with the remainder having no trend. For phosphorus, 44% of the sites had improving trends, 33% had degrading trends, and the remainder had no trend. These results are used to assess the water quality response to nutrient and sediment restoration efforts and target where future restoration can be most effective. Additional information can be found here.


There are multiple factors affecting attainment of water quality standards and response of nutrients to management actions in the watershed. The Chesapeake Bay Program water quality standards indicator showed a third consecutive year of degrading results but is influenced by the amount of pollution washed into the Bay each year. There are mixed results in the watershed response to management actions based on the monitoring sites located throughout the watershed. Studies are improving the understanding of the factors affecting water quality response to nutrient reduction efforts in the watershed. Recent studies identified water quality improvements resulting from point source upgrades and reduced air deposition of nitrogen, but management challenges are recognized in addressing nonpoint sources of nutrients in agricultural and urban lands delivered to rivers and the Bay.

Learn About Factors Influencing Progress

Management Strategy

To achieve the Water Quality Standards Attainment and Monitoring outcome, participating partners have committed to:

  • analyzing water quality trends in the Chesapeake Bay and its watershed,
  • explaining the factors affecting water quality trends in the Bay and its watershed,
  • enhancing Chesapeake Bay Program models using our improved understanding of water quality trends,
  • informing management strategies to improve water quality, and
  • adhering to the TMDL Accountability Framework.

Assessing progress toward achieving the outcome will occur through analysis of data collected from monitoring networks that track river flow, nitrogen, phosphorus and sediment in the watershed; air deposition of nitrogen and phosphorus; water quality conditions in tidal waters relative to established water quality standards; conditions of tidal habitats; changes in climate and the health of living resources.

As part of the Chesapeake Bay Program’s partnership-wide implementation of adaptive management, progress toward this outcome was reviewed and discussed by the Management Board in September 2022. It will be reviewed and discussed by the Management Board again in August 2024.

Download Management Strategy (.pdf)

Logic & Action Plan

Chesapeake Bay Program partners have committed to taking a series of specific actions that will support the management approaches listed above.

Learn About Logic & Action Plan

Participating Partners

The Water Quality Goal Implementation Team leads the effort to achieve this outcome. It works in partnership with the Scientific, Technical Assessment and Reporting Team.

Participating partners include:

  • State of Delaware
  • State of Maryland
  • State of New York
  • Commonwealth of Pennsylvania
  • Commonwealth of Virginia
  • State of West Virginia
  • District of Columbia
  • Chesapeake Bay Commission
  • Natural Resources Conservation Service (U.S. Department of Agriculture)
  • U.S. Army Corps of Engineers
  • U.S. Department of Defense
  • U.S. Department of Homeland Security
  • U.S. Environmental Protection Agency
  • U.S. Geological Survey