Discovery comes as Riverkeeper launches monitoring tool

On Sept. 10, the environmental group Riverkeeper launched a water quality portal with an interactive map that shows where it's safe to swim and fish in the Hudson River.

It also indicates where sewage is more likely to overflow during heavy rains, the location of concentrated animal feeding operations (a frequent source of pollution) and the presence of bacteria that can form harmful algal blooms that are dangerous to people and pets.

The timing, unfortunately, was perfect. Two days later, the Cary Institute of Ecosystems Studies in Millbrook announced that it had documented the largest harmful algal bloom (HAB) in at least 40 years of monitoring, stretching across the river from Kingston to Staatsburg.

The discovery comes at the tail-end of a busy summer for blooms, with similar (although smaller) ones occurring elsewhere, including Beacon's Long Dock Park in August. Earlier this summer, Putnam County shut down 14 beaches due to blooms.

"The algal bloom points out both the importance of having historic data" to monitor conditions and consider responses, said Tracy Brown, president of Riverkeeper, which is based in Ossining and Kingston. The nonprofit will soon update its portal to show the effects of climate change on the river.

Pollution and stormwater run-off can cause HABs, but Chris Solomon of the Cary Institute, one of the researchers who discovered the large bloom, said its origins are not clear. He said it's likely that drought and warm water were involved, as they were in the creation of an HAB that appeared in Beacon's Melzingah Reservoir during the hot, dry summer of 2021.

Both of those factors are likely to become more common in the Hudson Valley. "Increasing water temperatures, air temperatures and droughts are the things that are triggering the algal blooms we're seeing now," said Brown. "Climate change is here, and it's unfolding in real time."

The surface area of the HAB near Kingston isn't its only notable feature, said Solomon. Blooms usually only form in slack water, so it's unusual to see one stretch out across the free-flowing river instead of hugging the shore. And the bloom is unusually wide and deep. "Anywhere we looked in the water column, the algae was quite dense," said Solomon. Satellite imagery taken earlier this week showed that the bloom has continued to grow.

HABs can cause skin irritation, gastrointestinal symptoms and, in more potent cases, neurological damage and death.

Riverkeeper partners with the National Oceanic and Atmospheric Administration to collect data for its portal, but NOAA, like many federal science agencies, has been targeted by the Trump administration for cuts. Senate Minority Leader Charles Schumer (D-NY) secured $250,000 to launch the portal, but Brown expects there may not be more funds coming.

Earlier versions of the portal highlighted that "the open Hudson tends to be cleaner than a lot of the tributary rivers and streams," said Brown. "That flies in the face of people's assumptions. They think, 'Oh, this beautiful little stream going through my local duck pond is going to be nice to swim in as opposed to the big, nasty Hudson.' People were swimming in Rondout Creek in Kingston because they thought it would be cleaner than Kingston Point Beach, on the Hudson."

The Riverkeeper portal is one of several new monitoring tools. This past summer, Bard College unveiled an air monitoring site and the Open Space Institute debuted maps that track how much carbon America's forests are sequestering.

Riverkeeper's online portal is at data.riverkeeper.org. To report a Harmful Algal Bloom, see bit.ly/HABform or email [email protected]. The state also maintains a map of HABs at tinyurl.com/nys-hab-map.