A rust tide in Flanders Bay in 2013. Courtesy photo: Auxiliary Coast Guard

A toxic algae bloom known as rust tide has returned to local waterways, showing up in bays from Riverhead to East Hampton.

According to Dr. Chris Gobler of the School of Maritime and Atmospheric Sciences of Stony Brook University, the bloom is a seasonal event, but when levels of the Cochlodinium polykrikoides organism rise to thousands of cells per milliliter, it becomes toxic to marine life.

“We’ve seen low levels lingering around in different locations for the past month or so, but since the weekend the levels have really popped up,” he said.

Last week’s heavy rainfall was only part of the reason for the bloom, Gobler said.

“There are multiple mechanisms that cause fish kill with this algae,” he said. “Lowered levels of oxygen driven by the bloom is one way, but the organisms also secrete a mucus that is problematic for shellfish. They also release free radicals that do damage to almost any tissue and specifically fish gills. It prohibits their gills from functioning optimally.”

The algae is so toxic it can kill small fish in a matter of minutes, he said.

Additionally, excessive levels of nitrogen in the water are well-established causes of toxic blooms. Farm fertilizer and cesspools contribute to increased nitrogen levels in the bays.

The rust tide usually lingers through into September, Gobler said, and then once things cool down it will disappear.

“It can wax and wane a bit – it likes the warmer temperatures,” he said. “It’s going to depend on how things play out over the next month or two. If we have consistently warm weather with doses of additional rainfall, it’s going to stick around. If it suddenly turns cooler, it may go away.”

Gobler stressed that the algae is not dangerous to humans and since it kills fish so quickly, any live fish that are caught would be safe for consumption.

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