Blogs > Water Quality > Wallkill River harmful algae: intense one summer, gone the next – but why?

Wallkill River harmful algae: intense one summer, gone the next – but why?


A sample of water from the Wallkill River taken in 2016, during a Harmful Algal Bloom. (Photo by Dan Shapley / Riverkeeper)
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A sample of water from the Wallkill River taken in 2016, during a Harmful Algal Bloom. (Photo by Dan Shapley / Riverkeeper)

Riverkeeper’s Water Quality Program recently wrapped up an intensive sampling of part of the Wallkill River for key indicators related to Harmful Algal Blooms.

The good news: Unlike in 2015 and 2016, there was no Harmful Algal Bloom documented in 2017. The better news: We and our partners have gathered important baseline data that will help us understand why – and ultimately how to prevent Harmful Algal Blooms in the future.

In August of 2015, the Wallkill River around New Paltz turned bright green from a Harmful Algal Bloom that covered roughly two miles of the river. In 2016, a bloom occured in August in the same stretch of river, ultimately affecting 30 miles of the Wallkill for as long as two months, rendering long stretches of the river unfit for recreation, and risky for other uses. In the words of Jason West, the Executive Director of the Wallkill River Watershed Alliance, it became, “…a river of poison.”

These algae blooms are harmful because the algae – or more accurately, cyanobacteria – can produce toxins that, when ingested, can cause illnesses ranging from upset stomach to neurological damage. Dogs can be particularly vulnerable, and have been known to die from the double-dose exposure of swimming followed by grooming. These toxins affect people, as well as animals and wildlife. When there is an active bloom in a waterbody, people and their animals should avoid contact with the water.

While there are still questions about the particular conditions that cause harmful algal blooms, in most cases the ingredients that fuel them include high temperatures, still water and excess nutrients. Harmful algal blooms, or HABs, are becoming more common throughout the United States, and the world. As HABs increase in frequency they can threaten drinking water supplies, wildlife, and recreation. Climate change, which is increasing both temperatures and the intensity of storms that wash nutrients from farms, lawns and streets into streams and lakes, is thought to be one factor fueling their increase. Experts predict that HABs will only become more common as the planet continues to warm, making understanding their triggers more critical than ever. 

This year, from July to October, Riverkeeper, in conjunction with our partners at the Wallkill River Watershed Alliance and several community scientists gathered 120 samples from four locations twice weekly in, up and downstream of New Paltz, where blooms have been observed in both 2015 and 2016.  We took temperature measurements, and are having the samples analyzed for nutrient concentrations. These data will help us and our partner, the Wallkill River Watershed Alliance, to better protect and advocate for the Wallkill. Three Ph.D. scientists who volunteer for the Wallkill River Watershed Alliance are involved in the study: John Gotto lead the design of the sampling program, and will analyze the water quality data, Neil Bettez will measure nutrient concentrations in the samples at Cary Institute, and Jillian Decker and her students at SUNY Rockland will analyze samples to understand changes in algal communities over time under different conditions.

The Department of Environmental Conservation also conducted extensive sampling at several points in the Wallkill River in 2017, including measurements relevant to harmful algal blooms. This sampling was part of routine monitoring conducted by DEC, but included more extensive testing because of the recent Harmful Algal Blooms and community concerns about them.

We want to ensure the Wallkill, a large tributary of the Hudson, can be enjoyed for paddling and other recreation. The data gathered in 2017 will help inform plans to achieve that.

On a local level there are still plenty of ways take action to reduce nutrient pollution. To learn more about what you can do, check out this factsheet

To support the work being done on HABs please consider supporting Riverkeeper or the Wallkill River Watershed Alliance with a tax deductible donation.

The Harmful Algal Bloom monitoring project was funded by the NYS Environmental Protection Fund, via the DEC Hudson River Estuary Program.

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