On April 7, 2000, at approximately 6 pm eastern daylight time, a leak was detected in a 12-inch underground pipeline that supplies oil to the Pepco Chalk Point generating facility in Aquasco, Maryland. Approximately 140,000 gallons of fuel oil spilled from the ruptured pipeline into Swanson Creek, a small tributary of the Patuxent River. The spilled oil was a mix of Number 6 fuel, the oil normally transported by the pipeline to generate electricity, and Number 2 fuel, much lighter oil that was being used to flush the pipeline as part of a cleaning process.

Pepco, the Environmental Protection Agency (EPA), and Maryland Department of the Environment began containment and clean-up following the April 7 spill. Initial response actions were focused in Swanson Creek, and included deployment of protective booms to limit the spread of oil and the use of vacuum trucks and tanks to collect the discharged oil. On the night of April 8, severe weather conditions caused oil to breach and/or crest over the booms that had been deployed, spreading oil into the Patuxent River, approximately 17 linear miles downstream. About 40 miles of environmentally sensitive downstream creeks and shorelines along the Patuxent River were oiled. Marshes were observed to have been exposed to black oil or sheen, birds were observed to have been oiled, and survey teams collected dead birds, fish, muskrats and other animals.