Blue-Green Algae Bloom in Georgica Pond

Update, Aug. 13: There will be no crabbing in Georgica Pond for 21 days, by order of the East Hampton Town Trustees, who acted on Tuesday in response to the dense bloom of cyanobacteria, or blue-green algae, that developed last week.

It is the second consecutive year that the trustees have closed the pond to the taking of crabs, though this year the closing comes a month later than in 2014, likely because the pond has been open to the Atlantic Ocean for much of 2015, resulting in increased tidal flushing.

Originally, Aug. 10: A dense bloom of cyanobacteria, or blue-green algae, has developed in Georgica Pond in East Hampton for the second consecutive year, and the New York State Department of Environmental Conservation is warning against exposure to the water.

Anabaena, the genus of cyanobacteria blooming in the pond, can produce gastrointestinal toxins and neurotoxins. Exposure can cause vomiting or diarrhea, skin, eye, or throat irritation, nausea, or allergic reactions or breathing difficulties.

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. The East Hampton Town Trustees, who manage many of the town's beaches, waterways, and bottomlands on behalf of the public, are expected to decide on Tuesday whether or not to close the pond to the harvesting of crabs, as they did last year. The prohibition remained in effect from July 2014 into the fall.

Late last week, levels of blue-green algae in Georgica Pond exceeded 100 micrograms per liter, according to Christopher Gobler of Stony Brook University, who has led a water-monitoring program of trustee-managed waters in conjunction with the trustees for the last three years. The D.E.C. has set a threshold level of 25 micrograms of blue-green algae per liter as the concentration above which a public notice is issued.

A cyanobacteria bloom in Fort Pond in Montauk was discovered last month after two dogs that had been in the water experienced gastrointestinal illness. In 2012, a dog died after exposure to the waters of Georgica Pond.

Harmful algal blooms such as cyanobacteria thrive in brackish, low-salinity water. Georgica Pond had been opened to the Atlantic Ocean for much of 2015, and Dr. Gobler and the trustees had hoped that the tidal flushing resulting from the extended opening would discourage algal blooms. According to a release prepared by Dr. Gobler and issued by the trustees on Monday, however, "the naturally rapid flow of stream and groundwater into the pond progressively drove the salinity levels down from 31 PSU (practical salinity units) in late June 2015 to below 14 PSU by early August." Certain types of blue-green algae can grow at salinities of 15 PSU and lower.

In recent weeks, cyanobacteria blooms have persisted in Wainscott Pond in Wainscott, Maratooka Lake in Mattituck, and Agawam Lake and Mill Pond in Southampton, according to the D.E.C. Levels of cyanobacteria, and associated toxins, were particularly high in Agawam Lake.