Not all that bright green stuff floating on the water is harmful

Harmful Algae Bloom, Rondout Creek at the DEC fishing access site on Creek Locks Road in the Town of Ulster, Sept. 26, 2016 (Photo by Jen Epstein / Riverkeeper)
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While we have been highlighting the Harmful Algal Bloom on the Wallkill River, we want people to aware that rafts of bright green duckweed that are visible on the Hudson River and elsewhere at this time of year may look similar, but are not harmful.

We and the Wallkill River Watershed Alliance have documented cynaobacteria for at least 60 days on a 30-mile stretch of the Wallkill River, and a portion of the Rondout Creek downstream of the Wallkill River confluence. The extent and location of the algal bloom has shifted over time, but high toxin levels have been recorded on several occasions from this harmful type of algae. People are urged to avoid contact with the water, and to keep pets and livestock away from the water as well.

Harmful Algae Bloom, Rondout Creek at the DEC fishing access site on Creek Locks Road in the Town of Ulster, Sept. 26, 2016 (Photo by Jen Epstein / Riverkeeper)

Duckweed, a tiny plant, on the other hand is not harmful, though it too appears strikingly bright green. We haven’t seen evidence of Harmful Algal Blooms in the tidal reach of the Rondout Creek or Hudson River. Duckweed is evident throughout portions of the Mohawk River and Hudson River, based on observations from Capt. John Lipscomb’s most recent patrol. Read his 2015 blog post about its seasonal appearance on the Hudson..

Duckweed on the Hudson River, September 2015. (Photo by John Lipscomb / Riverkeeper)