Philadelphia -- Test results of water samples taken from the Anacostia River show that a black substance that has plagued a portion of the river since mid-August is a rare algal bloom, the U. S. Environmental Protection Agency announced today.
Initial testing by biologists from EPA and the Maryland Department of the Environment ruled out that the discoloration was a petroleum product or other hazardous substance. EPA also did not identify any apparent stress to fish, birds or plants from the algal bloom, known as a dinoflagellate, or more specifically as Gymnodinium.
Biologists determined that water conditions including temperature and nutrients in the water likely contributed to the rapid spread of the algae in the river. Based on recent EPA inspections, at least 75 percent of the bloom has already dissipated, and EPA expects the recent rains and cooler temperatures to cause the algae to completely die off.
Biologists said dinoflagellate blooms are rare in fresh water, such as the Anacostia River, but are common in estuaries of the Chesapeake Bay that have higher salt content.
The Washington, D.C. Department of Environment requested EPA assistance to determine the nature of the material after the U.S. Coast Guard eliminated oil as a source. D.C. Department of Environment officials will continue to monitor the algae in the river.