1914

• The Washington, D.C. sewer system carries wastes from 340,000 people to the Potomac and Anacostia Rivers.
• The United States Public Health Service study of pollution in the Potomac finds the river in "generally good condition" with "ample dissolved oxygen."

1916

• A survey of the Potomac notes that submerged aquatic vegetation (SAV) covers the Potomac along both banks, except for the central channel.

1930

• The Washington Suburban Sanitary Commission, serving Prince George's and Montgomery counties, connects its sewer system to the Washington, D.C. sewer system.
• George Washington Memorial Parkway opens to preserve natural areas along the Potomac River.

1932

• Untreated wastes flowing into the Potomac River cause bacterial contamination that forces the closing of the river for swimming from Three Sisters Island to Fort Washington. Low dissolved oxygen levels between Geisboro Point and Fort Foote endanger fish.

1938

• Blue Plains wastewater treatment plant is completed, with a capacity of 130 million gallons per day (mgd) in the primary treatment facility. The plant will treat wastewater for Washington, D.C. residents.