Potomac and Local Water Resources

The region’s huge investments in improving wastewater treatment have yielded significant progress, such as improved water quality in the Potomac River. For example, dramatic decreases in the amount of nitrogen and phosphorus discharged by wastewater treatment plants (WWTPs) have led to a decline in harmful algal blooms in the upper Potomac estuary and a rebound in plants and animals that live in this portion of the river, such as submerged aquatic vegetation and American shad.

To assess how effectively investments in wastewater treatment and stormwater management infrastructure are working, COG analyzes water quality in the Potomac River in support of the region’s local governments and water utilities that operate WWTPs and manage stormwater programs. COG support includes coordinating with state and local governments, universities, and scientists from around the region to monitor and provide up-to-date information that is relevant to the Potomac River. All of this technical work is regularly presented to the Water Resources Technical Committee (WRTC), and some of the associated analysis is outlined below.

Regional Potomac Water Quality Factsheets

COG prepared a Potomac Water Quality Factsheet entitled Potomac Water Quality in the Washington Region noting the many significant improvements in overall water quality and some living resources - due primarily to the significant investments by at the region’s WWTPs,as well as ongoing challenges due to continued growth in the region, and the need to address increased stormwater issues. 


Gunston Cove, Fairfax Virginia

Potomac River Monitoring at Chain Bridge – Data Analysis

In 1983, COG established an automated fall line monitor at the Chain Bridge on the Potomac River.  The Chain Bridge monitoring station is operated by Virginia Tech’s Occoquan Watershed Monitoring Laboratory (OWML) with funding from COG’s members.

Due to the number of streams discharging into the Bay watershed, and the changing composition of runoff due to storm events, it is challenging to monitor an individual river’s nutrient and sediment contributions to the Bay. However, with careful selection of sampling locations and times, it is possible to characterize pollutant inputs from a segment of the Potomac over a range of conditions.

The Chain Bridge station is part of an extensive network of monitoring stations throughout the Chesapeake Bay. The network of rivers being monitored were selected to encompass runoff from as much of the Bay watershed as possible, covering a range of different runoff sources to the Bay and its tributaries.  Since the fall line designates the transition from the Potomac River’s free flowing to its tidally influenced section, monitoring at the Chain Bridge location allows estimation of the quality and quantity of upstream nutrient and sediment loads to the Potomac estuary and the Chesapeake Bay.

The Chain Bridge station is also part of a historical data set. Since data collection began in 1983, there have been nearly 35 years of water quality data collected for the fall line of the Potomac River. Because long-term water quality trends can only be established when taken in the context of decades and the broader watershed, these sorts of databases are important for analysis.

For additional information about the program and data analysis: 

Chain Bridge Monitoring Program Fact Sheet
Chain Bridge Data Analysis Report


Potomac Water Quality Monitoring Programs

COG’s partners in gathering and analyzing water quality data for the Potomac, as well as local water quality monitoring efforts includes:

Maryland Department of Natural Resources
Virginia Department of Environmental Quality
District Department of Energy and Environment
Occoquan Watershed Monitoring Laboratory
George Mason University
University of Maryland Center for Environmental Science
United States Geological Survey