Thomas Warren, wtop.com
WASHINGTON - Officials at Rock Creek Regional Park are urging visitors to avoid Lake Needwood after a toxic substance was found in the water.
That substance, microcystin, was produced from blue-green algae that was detected in lake water.
Maryland follows the World Health Organization's 10 parts-per-billion threshold for safe algae levels in recreational water sources. Anything above that is deemed hazardous, and the public must be warned to avoid the waters. Lake Needwood exceeded that threshold, therefore warning signs have been placed throughout the park.
"Primarily it attacks the liver of whoever, or whatever ingests it," says Doug Redmond, Natural Resources Manager with the Maryland-National Capitol Park and Planning Commission's Montgomery County division.
Though the liver damage can be severe, no human deaths from the microcystins have ever been reported, according to the California Environmental Protection Agency.
Excessive algae levels in the lake were first reported by a park visitor in 2009, according to park officials.
"He happened to be an expert in blue-green algae," Redmond says.
Extreme exposure can also cause skin irritation.
Swimming, boating and waterskiing can put a person at risk of being exposed to microcystins. Swimming is prohibited in Lake Needwood.
People who walk their dogs along the lake are what concerns park officials most.
"If the dogs drink the water, they can very well be harmed if they ingest a significant amount of the toxin," Redmond says.
Fishing is permitted in the lake. If any fish ingest the toxin, it's concentrated in their internal organs making fish safe to eat, despite the warning.
"People can eat the fish as long as they're eating the muscle meat."
The park supplied samples for the last water test that was done in July, according to the Maryland Department of the Environment.
Another water test is planned before the end of the year.
Until then, Redmond urges caution when near the lake.
"People should, for the most part, just avoid excessive contact with the water," Redmond says. "Keep dogs from drinking the water, and keep children out of the water."
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