Scientists explain what happened last summer, whether the river is safe, and why more blooms may be coming.
Last summer, researchers conducting routine monitoring on the Hudson River began encountering something they had never seen at that scale: a harmful algal bloom extending through a broad section of the river around Kingston.
The bloom, identified as Microcystis, was the largest observed during nearly 40 years of monitoring by the Cary Institute of Ecosystem Studies. At some locations, concentrations of the cyanobacteria exceeded recreational safety guidelines. The bloom persisted for several weeks and was visible from shore, tinting parts of the river green from Poughkeepsie toward Catskill.
At an August 5 forum at Cary Institute in Millbrook, Harmful Algal Blooms: What You Need to Know, scientists and officials from Cary, Riverkeeper, the New York State Department of Environmental Conservation, and the state Department of Health discussed what happened, what remains unknown, and what Hudson Valley residents should do when the water turns green.
Here are seven takeaways.
1. Last summer’s bloom was genuinely unusual
Harmful algal blooms, or HABs, are concentrations of cyanobacteria, microscopic organisms that thrive under certain environmental conditions. Despite the name, cyanobacteria are not true algae, though their appearance is similar. Some produce toxins, including microcystin, the cyanotoxin most commonly detected in New York.
HABs are familiar in lakes and ponds, where warm, nutrient-rich and relatively still water creates favorable conditions. Until recently, scientists considered a bloom of this magnitude unlikely in the Hudson, where currents, tides, turbidity, and the constant movement of water should make it difficult for cyanobacteria to become established.
Last summer’s bloom challenged that assumption. Cary aquatic ecologist Chris Solomon said the concentrations recorded during the event ranked among the highest levels of algal abundance found in the institute’s decades-long Hudson River record. “This bloom that we had last year seems to have been quite unusual,” Solomon said.
2. Scientists don’t know why it centered around Kingston
The bloom was particularly intense in the Kingston area, where several major tributaries—the Rondout, Wallkill, and Esopus—enter or approach the Hudson. Those waterways carry nutrients and may contain backwaters where cyanobacteria can develop, but researchers have not identified any one tributary as the source.
Riverkeeper’s sampling offered some evidence that the bloom was moving from the Hudson into Rondout Creek, not spilling out of the creek into the river. The Wallkill, which has experienced its own extensive blooms, was not blooming immediately before the Hudson event. “We don’t know,” Solomon said when asked why Kingston became the center of the bloom.
One possible contributor was drought. With less freshwater flowing downriver, water remained in each portion of the Hudson longer, giving cyanobacteria more time to grow before being flushed toward the ocean. The drought also pushed the salt front unusually far north, potentially changing how nutrients moved through the estuary. Warm temperatures added another favorable condition.
Researchers are now trying to understand how those factors interacted. They eventually hope to predict where and when future blooms will occur.
3. Treated drinking water remained safe
Although toxin levels in untreated Hudson River water exceeded recreational guidelines at some locations, tests of finished water from municipal treatment plants found very low toxin concentrations, safely below established health guidelines.
Conventional drinking-water treatment is highly effective at removing cyanobacteria and their toxins. During a bloom, plant operators can increase testing and adjust filtration, coagulation, and disinfection processes according to the condition of the incoming water.
State health officials said New York has not experienced a public drinking-water interruption resulting from a HAB. At the forum, Department of Health outreach and education director Gena Gallinger said the HAB-related illnesses reported to the state have overwhelmingly resulted from recreational contact, not municipal tap water.
Private systems drawing untreated water directly from a river, lake, or pond are another matter. State officials advise against using untreated surface water for drinking, cooking, or making ice, whether a bloom is visible or not. Boiling does not remove cyanobacteria or their toxins.
4. Swimming and shoreline exposure present the greater risk
Regulated bathing beaches have operators trained to recognize blooms and close swimming areas as soon as suspicious water appears. They do not wait for laboratory confirmation because blooms can shift rapidly and cause health effects whether or not tests detect toxins.
Along the Hudson, however, people commonly enter the water at boat launches, parks, docks, and other informal access points without trained staff or warning signs. Riverkeeper senior director Dan Shapley identified those locations as an important gap in the region’s public-warning system.
Exposure can occur through swallowing contaminated water, skin contact, or inhaling aerosolized droplets. Reported symptoms include itchy skin or eyes, sore throat, nausea, diarrhea, vomiting, allergic reactions, and breathing difficulties, particularly among people with asthma.
If exposed, rinse off promptly with clean water. Anyone experiencing symptoms should contact a healthcare provider.
5. If the water looks bad, stay out
Laboratory analysis can identify the cyanobacteria and toxins present, but people deciding whether to enter the water do not need to wait for test results.
Blooms may resemble pea soup, spilled paint, floating mats, surface streaks, scum, or clumps. Green is the most familiar color, but blooms may appear in other colors and can accumulate along beaches, rocks, and shorelines.
The state’s advice is summarized in three steps: “Know it, avoid it, report it.”
Because blooms move with wind and currents, one section of a water body may be affected while another remains clear. Gallinger advised recreating where the water looks clear and avoiding any suspicious patches. Suspected blooms can be submitted through DEC’s NYHABs reporting system, preferably with both a close-up photograph and a wider view showing the location.
6. Dogs face an especially serious danger
Animals often receive a much larger dose of contaminated material than people. Dogs may drink directly from the water, eat material along the shoreline, or lick cyanobacteria from their coats after swimming.
Symptoms can develop rapidly and may include vomiting, diarrhea, loss of appetite, stumbling, seizures, and convulsions. HAB exposure has caused pet deaths in New York.
Keep dogs away from suspicious water and rinse them thoroughly with clean water after a possible exposure. If symptoms appear, contact a veterinarian immediately.
Officials also cautioned against using water from an active bloom to water crops, wash fruits or vegetables, or supply livestock. Research into how cyanotoxins behave in agricultural settings is still developing, but the immediate recommendation is precautionary: If water appears affected, don’t use it.
7. Another Hudson bloom is likely
No one on the panel predicted that last summer’s conditions would return every year. But Solomon called it “reasonably likely” that significant blooms will recur as climate change and nutrient pollution continue to alter the river.
Heat and drought favor cyanobacteria, and the Hudson has already warmed over the past century. The most direct intervention available to policymakers is reducing phosphorus, a nutrient entering the river from sewage-treatment plants, septic systems, stormwater, agricultural runoff, and tributaries.
“We know the solution,” Shapley said. The challenge is putting it into practice.
Riverkeeper is calling for the state to finalize long-delayed phosphorus-reduction plans for the Wallkill and Mohawk rivers, establish a phosphorus threshold for the Hudson, analyze recent water-quality data against that threshold, and direct funding toward wastewater upgrades, septic replacement, stormwater controls, wetland protection, and other pollution-reduction projects.
Monitoring will also be essential. Last summer’s bloom was recognized and tracked because Cary, Riverkeeper, state agencies, and drinking-water operators were already watching the river. Sustaining that work will allow scientists to understand what triggered the bloom—and give riverside communities more warning when the conditions align again.
For now, the advice for river users remains straightforward: Look before entering, keep children and pets away from suspicious water, and report what you see. The Hudson is still swimmable, fishable, and drinkable after treatment. But after last summer, no one can assume that a flowing river is immune to harmful algal blooms.
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More headlines about “potential” HAB’s, which neglect to mention “blooms” in the Wallkill River have not been definitively ID’d in terms of actual species. This is both remarkable and scientifically reckless.
The WRWA has made it clear, since their formation, that HAB’s are their vector of interest: They’ve been trying desperately to see something which may or may not be present – and then, inexplicably, they stop short of specific identification… but they issue press releases anyway.
To a serious ecologist, this is troubling.
There are over 900 genera of freshwater algae described in North America, with thousands of individual species. The phylum cyanobacteria, under which a few of the HAB genera and species fall (along with innumerable other benign species) is poorly understood, at best, with fewer than half its possible species even described.
More than 99.99 percent of the thousands of species of algae in North America are harmless, and actually serve important functions toward healthier ecosystems. The hyperbole surrounding HAB’s in our region should be taken for what it is – the ecological equivalent of opening a box of baking soda, observing a white substance within, and calling it “potential” anthrax. It could be anthrax, but such an ID would be sensational, create panic, make great publicity and lead to great funding.
This form of “greenwashing” (a term I coined 30 years ago) relies on “biophobia” (fear of nature) to foment public panic, as opposed to working against truly dangerous anthropogenic threats such as pesticides and habitat destruction. The fight against man-made threats carries the risks of litigation and powerful enemies.
Riverkeeper understands profit and risk: More than half of the $5 million annual contributions it received in 2014 went to staff pay.
Riverkeeper’s staff scientist, Bill Wegner, was hired in 1999 after serving a federal sentence for smuggling endangered bird eggs. His hiring prompted an exodus of many of Riverkeeper’s original visionaries, including Riverkeeper’s president Robert Boyle, dramatically changing Riverkeeper’s ethical composition.
Riverkeeper’s treasurer resigned, stating that hiring Wegner was “…particularly inappropriate because his crime was an environmental one.”
Having worked with Wegner in the 1980s, I personally understood the severity and self-serving greed of his crimes against nature.
Riverkeeper isn’t alone: In 2010, I discovered the DEC water-quality policy-maker who consistently recommended one herbicide worked for an NGO whose largest funder was the manufacturer of that pesticide.
While HAB’s do exist, their potency and occurrence are frequently exaggerated: Panic, after all, is the friend of Profit.
Jay Westerveld is a field ecologist and founder of the New York Natural History Council.