If you head out for a paddle on the Peconic River this weekend, you’ll encounter something you may have never seen before.

A prolific bloom of an aquatic plant is overspreading the freshwater portion of the river, west of Peconic Avenue to approximately Forge Pond.

Its identity is yet to be confirmed by scientists and state environmental officials, who say they will be taking samples for examination and testing. Upon reviewing photos of the bloom this afternoon researchers at Stony Brook think it looks like a plant genus called Azolla, common name: mosquito fern.


Azolla reproduces rapidly, doubling its biomass in three to 10 days.

“It’s highly productive, especially in eutrophic waters,” according to Jen Goleski, a researcher working with Dr. Christopher Gobler of Stony Brook University.

Eutrophic waters are those especially rich in nutrients, such as nitrogen. The nutrients support growth of a plant like Azolla, which can cover an entire body of water. It can grow so thick that mosquito larvae breeding in stagnant water cannot penetrate it to reach the surface and die — so it is known as a natural larvicide, of sorts (hence the name “mosquito fern.”) That’s the good news.

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The bad news is when the plants die off and decompose, they produce even more nutrients and in such great quantities that they kill animal life by depriving it of oxygen. In other words, the already-high nitrogen levels in the Peconic River — which have lowered dissolved oxygen in the water causing fish kills — are likely to get even higher during the natural life cycle of this prolific invasive plant species.

Gobler said his team would need to get samples to confirm its identity. “We will look into this,” he said.

N.Y. State DEC staff will be collecting samples to identify what’s on the water surface, according to DEC spokesperson Aphrodite Montalvo. After reviewing photos sent to the DEC Region I office in Stony Brook by RiverheadLOCAL, DEC staff said they will visit the river to collect samples for identification and testing.


If the growth is Azolla, as Gober Lab members suspect, it poses no danger to humans. Some species of Azolla are actually used as biofertlizers for food crops, such as rice paddies in Southeast Asia.

Though it is an unusual sight in these parts — and considered a “rare” plant in New York — Azolla is “naturalized” in the Peconic River, according to plant experts. While it is an invasive, it is also listed by the state as a plant that is likely to become threatened in the near future.

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Denise is a veteran local reporter, editor, attorney and former Riverhead Town councilwoman. Her work has been recognized with numerous awards, including investigative reporting and writer of the year awards from the N.Y. Press Association. She is a founder, owner and co-publisher of this website.Email Denise.