A river shouldn’t turn fluorescent green and produce toxins.

Yet, that’s what happened on the Wallkill River this year, with a harmful algal bloom documented from August 24 through at least October 24, affecting as much as 30 miles of the river from Montgomery in Orange County to Sturgeon Pool in Ulster County, and into the Rondout Creek downstream of the Wallkill’s confluence. Outlying blooms were also observed on August 15 in the Rifton area and on September 14 in the National Wildlife Refuge at NY-NJ state line.

The affected areas of the Wallkill River and Rondout Creek have many public, private and informal access points used for boating, fishing and swimming. A private beach on Sturgeon Pool was closed on recommendation of the Ulster County Department of Health, the DEC posted warning signs at several boat launches and fishing access sites, a kayaking rental business had to turn customers away from its usual New Paltz launch site, and public paddles scheduled by the Wallkill River Watershed Alliance, including one as part of the Hudson River Valley Ramble, had to be canceled. The river is designated for recreational use in this stretch, and its use was severely impaired.

The cyanobacteria bloom was documented with visual and photographic evidence, microscopic analysis by scientists associated with the Wallkill River Watershed Alliance, and through both microscopic and toxin analysis by the SUNY College of Environmental Science and Forestry, in collaboration with the NYS Department of Environmental Conservation.

These analyses confirmed the presence of cyanobacteria (also known as blue-green algae), and on several occasions the toxins produced by cyanobacteria, and at levels many times the DEC thresholds for public notification based on potential risk from exposure during recreational use of the water. One sample registered at 25-times the threshold level, while another was 86-times the DEC’s recommended toxin threshold. Toxins produced by cyanobacteria can be harmful to people, dogs or other pets, livestock and mammalian wildlife. Exposure may result from ingestion, skin contact or inhalation. Health effects from exposure may include skin irritation, fever, nausea and vomiting, or more serious health problems, including neurological and liver damage. The most serious symptoms are likely to result from exposure by ingestion. In addition to human health effects, large algal blooms can stress or kill fish and other aquatic life, particularly as algae die and decompose, consuming oxygen that aquatic life needs to survive.

While algae are a natural part of any river ecosystem, a long-lasting widespread harmful algal bloom (HAB) of this type in a river is not a purely natural condition. Conditions that lead to algal blooms such as this include high temperatures, slow or stagnant water, and excess nutrients in the water that could come from sewage (both treated and untreated), urban runoff, and runoff of fertilizers from farms and lawns. The hot summer and prolonged drought conditions set the table for the bloom, and scientists have warned that warmer temperatures and altered precipitation patterns due to climate change will produce these conditions more frequently. But not every river in our region was affected, indicating that the Wallkill has specific local problems that can and should be addressed to reduce the risk of future harmful algal blooms.

Whereas many lakes and ponds have been documented with harmful algal blooms in this and other summers, only two other rivers in the state reported suspicious algae blooms this year. We aren’t aware of any other river in New York State affected to the degree - in duration or extent - that the Wallkill was.

The DEC recommends public notification to avoid contact with the water as soon as algae that may be harmful is observed. After the DEC and SUNY ESF “confirmed” the bloom first through microscopic analysis to the genus level, and later by measuring high toxin levels, Riverkeeper and the Wallkill River Watershed Alliance issued press releases and shared details with municipal leaders, after consultation with the DEC, to inform the public. Several newspaper, television, radio and online news outlets responded with stories.

Documenting this environmental problem is a community effort, as is communicating about it to the public, agencies and municipal leaders.

Riverkeeper began coordinating community science river monitoring on the Wallkill from its mouth to the New York-New Jersey state line in 2012, as part of our ongoing pathogen monitoring project. We expanded the effort in 2015 into the river’s headwaters in New Jersey.

In August 2015, members of the Wallkill River Watershed Alliance observed bright green algae affecting about a two-mile stretch of the Wallkill River through New Paltz, and microscopic analysis by Jillian Decker, Ph.D., of SUNY Rockland, an Alliance board member, confirmed the presence of potentially harmful cyanobacteria.

With funding from the Environmental Protection Fund, via a grant from the Hudson River Estuary Program, we were able to help the Wallkill River Watershed Alliance launch a community algae observation project, and expand our routine community monitoring on the Wallkill River to include collection of samples for analysis of algae by Decker and John Gotto, Ph.D., of SUNY Ulster, and of nutrients by Neil Bettez, Ph.D., an Alliance board member. These data will be analyzed this winter, and should help us understand much more about the underlying causes of the harmful algal bloom.

The project has effectively connected a network of community scientists, the members and scientists of the Wallkill River Watershed Alliance, and DEC and SUNY ESF experts in harmful algal blooms to document and gather data along the full 83-miles of this major Hudson River tributary, and in more than a dozen of its tributaries.

Just as documenting the problem has been a community effort, so will be finding solutions. Riverkeeper has taken numerous legal actions to protect the Wallkill River over its 50-year history, including lawsuits to stop the expansion of a landfill into wetlands and to reduce raw sewage overflows into the river. But tackling a problem like this will take a true watershed approach. The Wallkill River Watershed Alliance, which formed in 2015 and is the recipient of one of the Hudson River Watershed Alliance’s 2016 Watershed WaveMaker Awards, is assembling the data, expertise and people to do just that.