NEW YORK (CBSNewYork) — Scientists say they now know what caused the large fish kills in the Peconic River on Long Island.

As WCBS 880’s Sophia Hall reported, 300,000 fish and 100 turtles died during three separate fish kills in the Peconic River in Suffolk County.

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Scientists said a spike in algae blooms, due to increased nitrogen levels, are to blame.

Adrienne Esposito, with the Citizens Campaign for the Environment, said the higher nitrogen levels are due to over population.

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“The solutions are treating sewage before it enters ground water, and surface water,” she said.

County Executive Steve Bellone put a plan in motion to convert homes that have cess pools. Instead, the homes will be attached to a sewer system, which would prevent the waste from polluting ground water.

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“The plan that’s being implemented in Suffolk County is critically important. If we don’t get it done, we may not be able to be sustainable as an island,” Esposito said.