The second large fish kill in two weeks has inundated parts of the Peconic River with thousands of dead bunker baitfish after oxygen levels in the waterway clocked in at zero.

Marinas on the northeast side of the river have been swamped with the fish, Riverhead Supervisor Sean Walter said Monday. "We're at a loss to try to get these fish out," he said. "It's hugely problematic."

Dan Battaglia, an administrator of the Riverhead Moose Lodge, where many of the dead fish have massed around large boats, said members woke to the massive die-off Sunday morning. "Who knows what's floating around in this water?" he said.

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Battaglia said officials from Gov. Andrew M. Cuomo's office and the state Department of Environmental Conservation visited the lodge last Wednesday after the fish kill two weeks ago, and planned to announce an action plan that included funds for upgrading the nearby sewage plant.

But, he said, officials sent a text message Thursday canceling the scheduled Friday event. Emily DeSantis, a spokeswoman for Cuomo, said, "We are watching this situation very closely," She said the administration will continue to work with Suffolk County and the DEC "to find ways to improve Long Island's water quality."

Walter said Riverhead has been providing information to Cuomo's office and the DEC about the fish kills, which officials have tied to increased nitrogen levels in the water.

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One expert said warming waters could exacerbate the problem. Several recent days have seen zero oxygen levels. "Water temperatures are going to go up and the natural background level of oxygen is going to go down," said Chris Gobler, professor at Stony Brook University's School of Marine and Atmospheric Sciences.

Two weeks ago, dead bunker massed nearby at Indian Island County Park and Indian Island golf course after oxygen levels dropped to zero.

Gobler said a dense algae bloom that has swelled in the Peconic waterway in recent days was likely the cause of the problem.

While algae are big producers of oxygen during sunny days through photosynthesis, he said, the massive blooms create large "microbial communities," including bacteria, that respire at night, depleting oxygen levels. Large fish populations can quickly deplete what little oxygen remains during the blooms as they mass in the Peconic. Decaying fish in the water from the previous die-off also likely increased bacteria levels, he said.

While working with state and county officials, Riverhead hasn't had the time yet to come up with an action plan of its own to understand the problem and prevent it.

Walter blamed a combination of predator bluefish chasing bunker upriver, an overabundance of the baitfish, also known as menhaden, and higher algae levels. He also noted that about 90 percent of homes in and around that area of the river and bay have septic systems, which, along with street runoff and other factors, helped boost algae levels.

Walter said that the Riverhead town sewage treatment facility doesn't appear to be linked to the die-off and that the town is in the process of upgrading the facility.

The town has been depending on volunteers to help remove the dead fish, Walter said.

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Battaglia of the Moose Lodge said, "We just called the town today and they said they'd get back to us. I hope they get a piece of machinery to get the fish out. They're going to need machinery and trucks."