Fine (but Not Georgica)

Owing to the continued presence of cyanobacteria, Georgica Pond will remain closed to the harvesting of crabs, the East Hampton Town Trustees determined at their meeting on Tuesday.

The trustees voted to close the pond to crabbing for 21 days on Aug. 11, shortly after a dense bloom of the harmful blue-green algae developed in the pond for the second consecutive year. Levels of cyanobacteria in the pond exceeded 100 micrograms per liter, according to Christopher Gobler of Stony Brook University, who has led a water-quality monitoring program of trustee-managed waters in conjunction with the trustees for the last three years. The New York State Department of Environmental Conservation, which warned against exposure to the water, has set a threshold level of 25 micrograms per liter as the concentration above which a public notice is issued.

All of the water bodies monitored by the trustees in conjunction with Dr. Gobler “look very, very good, except for Georgica,” Stephanie Forsberg, the trustees’ assistant clerk, told her colleagues on Tuesday. The cyanobacteria bloom has spread across the entire pond, she said, and has exceeded the maximum levels measured last year, when the pond was closed to crabbing from mid-July into the autumn.

Levels of microcystin, a class of toxins produced by some cyanobacteria that can cause serious damage to the liver, is present at 1 microgram per liter, a level that Dr. Forsberg characterized as “a drinking-water threat, but not a recreational threat.” Nonetheless, she said, “I think we should continue the closure.” The pond remains a popular site for paddleboarding and kayaking, said Sean McCaffrey, a trustee. “I don’t want to see it closed,” Dr. Forsberg said, “but I also don’t want to see the alternative — if somebody should fall ill.” The trustees voted unanimously to extend the closure for another 21 days.

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. Georgica Pond was open to the Atlantic for much of this year, allowing prolonged flushing. Consequently, the trustees believe, the pond remained free of harmful algal blooms this year until later than in 2014.

Dr. Forsberg also told her colleagues that at this time last year cochlodinium, or rust tide, was present in both Accabonac and Three Mile Harbors in East Hampton. “But those sites are clean and clear now,” she said. Rust tide is algae that can be fatal to shellfish and finfish, but is not harmful to humans when ingested.