1940

• The Interstate Commission on the Potomac River Basin and the Potomac Valley Conservancy District are created to protect the Potomac River Watershed.

1948

• Congress enacts the first Federal Water Pollution Control Act.

1951

• Low dissolved oxygen levels kill thousands of fish during the summer. The Washington Post calls the Potomac River, "an open sewer."

1956

• The levels of raw and partially treated sewage emptying into the Potomac River from Washington, D.C., are double what they had been in 1932.
• The Chesapeake Bay Bridge-Tunnel opens to carry traffic over and under 17.6 miles of water.

1965

• The Water Quality Act of 1965 passes, establishing a Federal Water Pollution Control Agency and requiring water quality standards.
• President Lyndon B. Johnson labels the Potomac "a national disgrace," and sets cleanup goals for 1975.