DOVER, N.H. (AP) – A popular pond for fishing, swimming and boating has been closed indefinitely due to potentially toxic blue-green algae.

Willand Pond, located in Dover and Somersworth, will remain closed until water quality tests show the algae level has diminished, which could take a few weeks or the rest of the summer.

The algae, Cyanobacteria, can be harmful to people and pets if ingested and can cause skin irritation. City Health Inspector John Carlson said the naturally occurring bacteria, which bloom and form surface scum when ample nutrients and sunlight are available, have begun to dissipate since city officials first learned of it Wednesday. But there is no way of knowing how long it will take to completely clear up.

“You’ve got to let nature take its course for the most part with this,” Carlson said. “The state will monitor it throughout the summer.”

Residents nearby have complained that the pond’s water level has risen dramatically in recent years, due in part to flooding this year and last year. Jody Connor of the state Department of Environmental Services, said the rising water most likely has contributed to the emergence of algae this year. Because the water level is higher than normal, vegetation that typically grows outside of the water has become submerged, Connor said.

As that vegetation decays, it releases excess amounts of phosphorous into the pond, a nutrient that allows blue-green algae to flourish.

The algae is naturally occurring in all of the state’s lakes, but rarely found on the Seacoast. Last year, a total of seven bodies of water were shut down due to algae, Connor said.

While another lake in Henniker is on the verge, Connor said Willand Pond is the first so far this year to be closed.

“Once it starts, it typically takes a while to diminish,” Connor said.

Exposure to the algae may cause symptoms including nausea, vomiting, diarrhea, mild fever and general malaise, according to DES, and more serious cases can lead to liver and central nervous system damage. If someone believes they have come into contact with the algae, they should wash themselves off with fresh water.

Police and fire officials spent much of Thursday afternoon knocking on doors of nearby homes and businesses to warn of the potential health hazards. Police tape was placed around entrances into the waters, and informational fliers were posted throughout the area.

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