DC Water has expanded its water quality testing initiative over a three-week period at high-use recreational areas along the Potomac River. This proactive measure is intended to complement the daily water quality sampling already underway following the sewer overflow caused by the Potomac Interceptor collapse that occurred in January and has since been repaired. The expanded testing comes in response to community feedback and provides additional information to residents and recreational users about current river conditions.

For more than two months, daily water quality monitoring has shown E. coli levels have remained within the typical range for recreational use—with normal historical fluctuations driven by rainfall, temperature, stormwater runoff, and other known factors—at all sampling sites outside the immediate overflow area. In the immediate areas (Lock 10 and Minnie’s Island), levels have also remained within the typical range, with expected fluctuations, for more than a month.  

As part of the enhanced testing, DC Water is conducting interval water quality sampling every two hours from 8:00 a.m. to 6:00 p.m. at several key locations on three consecutive Saturdays, which began last weekend on April 11. This schedule enables comprehensive monitoring throughout the day, helping to validate daily water quality results while increasing transparency for the public.

The sampling locations were chosen based on their popularity for a range of recreational activities on the river and include:

• Minnie's Island: A publicly accessible island in the Potomac River near Cabin John, Maryland, popular for nature-based recreation—especially paddling (kayak/canoe/paddleboard access), swimming, and wildlife viewing.
• Sycamore Island: A private island used by members and guests for boating, fishing, swimming, and picnicking.
• Lock 6 Feeder Canal: A favored destination for paddlers that includes a kayak slalom course frequently used for training by world-class and other competitive and recreational kayakers.
• Fletcher’s Boathouse: A popular recreation hub near Georgetown, offering boat rentals, fishing, and family activities; and one of the most visited recreation sites along the river.
• Three Sisters: An iconic cluster of rocky islands near the Key Bridge popular with boaters, paddlers and local adventure groups, and during low tide its sandbar serves as a “beach” for informal gatherings. It should be noted that samples are collected once on Saturdays at this location due to the need to access the middle of the river via boat.

Enhanced Water Quality Sample Results

Results from the first round of testing mirror the overall daily water quality findings, which continue to reflect the typical range for recreation with normal variability. Notably, all locations remained within normal range throughout the day, and no results indicate issues stemming from the previously contained overflow.

MPN = Most Probable Number 
*Consistent with public health and U.S. Environmental Protection Agency standards, swimming is not recommended when E. coli levels exceed 410 MPN/100 mL.

DC Water will perform additional sampling at the same locations, on Saturday, April 18 and again on Saturday, April 25.

Environmental Rehabilitation Update

Clean-up efforts continue in the C & O Canal, which was used as a bypass during the Potomac Interceptor repairs. Soil removal continues between locks 10 and 12, with work completed between locks 12 and 14.

Meanwhile, site preparations continue for the previously planned long-term rehabilitation which has been accelerated for more than 2700 linear feet of the interceptor in this area. Excavation work is ongoing at a third location for the rehabilitation work which will use a process called slip lining to insert new pipes into the existing pipe, to strengthen and reinforce the interceptor to like new condition.

Daily water quality testing continues to show E. coli levels within the typical range for recreation, with normal historical fluctuations attributed to rain, heat, stormwater runoff, and other known environmental factors. See the District Department of Energy and Environment webpage for more details.

Ongoing sampling is precautionary and intended to address community concerns, ensuring the highest standards of public health and safety.

For the Potomac River, historical water quality data shows E. coli levels may vary from a range as low as 10 MPN/100mL to as much as 5,000 MPN/100mL on a given day.

Daily Water Quality Sample Results

You can find more information about the environmental rehabilitation, get the latest news and information, and results of all the water quality testing on our Potomac Interceptor Response page.