Duckweed, algal blooms affect streams, rivers, ponds and lakes – Poughkeepsie Journal

Late summer means giving way to fall’s colors.

But one color that doesn’t make everyone’s favorite list is a layer of bright green floating on top of your favorite creek, river, pond or lake.

These rafts of green material can be innocuous in some cases, and quite nocuous in others.

If you happen across a scene that looks something like what my colleague, Poughkeepsie Journal reporter Amanda Fries, photographed recently from Bridge Street in Wappingers Falls, don’t be alarmed.

Chances are, it’s duckweed mixed with a few water chestnuts.

This time of year, the water chestnut beds in the middle and upper parts of the Hudson River estuary start to decay and fall apart.

Duckweed thrives around water chestnuts in calm waters, such as ponds and quiet coves, according to the state Department of Environmental Conservation.

If you get a big rainfall, it breaks up the beds. Rafts of water chestnuts and duckweed begin moving downstream.

Long plumes of green were seen last week moving down the Hudson River, past the Norrie Point Environmental Education Center and points further south.

“It’s nothing to worry about,” said Chris Bowser of the DEC’s Hudson River Estuary Program. “Just another sign of the river changing with the seasons.”

Algae photographed north of New Paltz on the Wallkill River on August 26, 2015

A more sinister carpet of green was observed recently atop the Wallkill River in New Paltz by members of the Wallkill River Watershed Alliance.

Turns out, it was algae.

“On the Wallkill, conditions are right for algal blooms, given that the Wallkill is known to have an excess of nutrients,” wrote Dan Shapley of Riverkeeper in a recent blog post about the sighting.

The nutrients feed algae during sunny, drought-like conditions, which produce stagnant water, particularly when coupled with dams, Shapley wrote.

Algae can absorb oxygen in the water, making a stream inhospitable to fish.

In an update to his blog post, Shapley reports that an analysis of the algae determined it is consistent with what the DEC calls an HAB — harmful algae bloom.

Blue-green algae, called cyanobacteria, are naturally present in lakes and streams in low numbers, according to the DEC.

But when concentrations of the algae become high, the associated odors and appearance can negatively impact the recreational value of a body of water.

Some of these blooms can also produce toxic algae, though the DEC says the reason why is not well understood.

Those who come in contact with the toxic blooms can suffer from symptoms that range from nausea, vomiting and diarrhea, to skin or throat irritation, allergic reactions or breathing difficulties.

Though these blooms can occur naturally, they become an issue when excess nutrients from farm runoff, lawn fertilizers and treated, sewer-system discharges flow into bodies of water.

A good example of this is Wappinger Lake, which has experienced degraded water quality over the last few decades due to excess phosphorous. When too much phosphorous flows into the lake, it feeds the algae.

Falls plan serves as model to save Wappinger Lake

Wappinger Lake is designated as “impaired” for bathing and “stressed” for fishing, boating, aesthetics and fish propagation, due to weed growth and turbidity.

The Village of Wappingers Falls is working with other municipalities to reduce the flow of phosphorous nutrients into the Wappinger Creek watershed, which feeds Wappinger Lake.

“Out There” appears every other week in My Valley. Reach John Ferro at 845-437-4816; jferro@poughkeepsiejournal.com; Twitter: @PoJoEnviro

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