President Theodore Roosevelt and John Muir
- The United States Public Health Service reports that "... at certain times of the year the [Potomac] river is so loaded with sediments as to be unfit for bathing as well as for drinking and cooking purposes. It contains fecal bacilli at all times..."
- The first biological survey is conducted on the Potomac River.
- President Theodore Roosevelt focuses national attention on protection of the nation's water and forest resources in his first State of the Union address.
- United States Geologic Survey reports that the turbidity in the Potomac River is 3000 parts per million (ppm) during floods and 15-20 ppm during a normal low flow.
- Eighty-four species of fish are found in the Potomac River and its tributaries
- 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."
- A survey of the Potomac notes that submerged aquatic vegetation (SAV) covers the Potomac along both banks, except for the central channel.
- 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.