Harmful Algae in Ponds
Less than a month after two dogs that swam in Fort Pond in Montauk experienced gastrointestinal illness, the State Department of Environmental Conservation reported a persistent bloom of cyanobacteria, or blue-green algae, in the pond and cautioned against swimming or wading in it. Pets and children should also be kept away from the water, according to the D.E.C.
On the South Fork, cyanobacteria also persists in Wainscott Pond in Wainscott and Agawam Lake and Mill Pond in Southampton, according to the D.E.C. Levels of cyanobacteria, and associated toxins, are particularly high in Agawam Lake.
While blue-green algae are naturally present in lakes and streams, an abundance, caused by warm water temperatures and a lack of tidal flushing, can lead to harmful blooms. Exposure can cause vomiting or diarrhea, skin, eye, or throat irritation, nausea, or allergic reactions or breathing difficulties.
The East Hampton Town Trustees, in conjunction with Christopher Gobler of Stony Brook University, have been monitoring waters under trustee jurisdiction for the past three years. While Fort Pond is not under trustee jurisdiction, Dr. Gobler’s lab analyzed a sample of its water on July 29. The sample, he wrote in an email on Monday, contained 100 micrograms of blue-green algae pigments per liter and 5 micrograms per liter of microcystin, a class of toxins produced by some cyanobacteria that can cause serious damage to the liver.
The World Health Organization has set an international standard of 1 microgram of microcystin per liter, and the D.E.C. requires that any water body with greater than 25 micrograms of cyanobacteria pigments per liter be listed on its statewide assessment site.
The analysis followed an earlier examination resulting from the dogs becoming ill. That analysis showed relatively low levels of blue-green algae, but also “a mix of the types of blue-green algae that are known to produce toxins including microcystis,” Dr. Gobler wrote to town, county, and D.E.C. officials.
At the trustees’ July 28 meeting, Diane McNally, the presiding officer, told her colleagues that waterways under trustee jurisdiction continue to be healthy, although Georgica Pond in East Hampton, which was closed to the harvesting of crabs and other marine life for much of last year due to a cyanobacteria bloom, was experiencing a dense accumulation of a macro algal bloom, or seaweed. The pond was open to the Atlantic Ocean for much of this year, which, she said, had had the desired flushing effect.
At the trustees’ prior meeting, on July 14, Stephanie Forsberg, the assistant clerk, had reported that the macro algal bloom in Georgica Pond had resulted in a drop in dissolved oxygen and in isolated fish kills.