Blogs > Water Quality > State begins first-of-its-kind Hudson River water quality assessment

State begins first-of-its-kind Hudson River water quality assessment


View more images on our Flickr site

Two-year study will shed light on certain important risks, including algal blooms, but won’t measure bacteria to indicate where water is safe for swimming.

A fundamental aspect of the Clean Water Act, now in its 50th year, is that governments must assess water quality in waterways to determine if they meet water quality criteria. Surprisingly, the Hudson River Estuary has never before been assessed in this way, leaving uncertain questions about whether it meets Clean Water Act criteria for safe swimming, fishing and drinking.

This month, the Department of Environmental Conservation (DEC) is partnering with the U.S. Geological Survey to begin a first-of-its-kind water quality assessment of 136.5 miles of the estuary between the federal dam at Troy and the confluence of the Harlem River at the northern border of Manhattan. If the data show any exceedances of Water Quality Standards, then the Clean Water Act requires actions to reduce pollution levels.

Carol Knudson of Columbia Lamont-Doherty Earth collects a water sample from from a Sea Tow vessel.The two-year assessment will help determine the quality of Hudson River water. The focus of the project is to measure river chemistry, to see if dissolved oxygen is sufficient to support aquatic life, for instance, or if certain contaminants like arsenic or cadmium exceed safe thresholds. It will establish some important baseline information about nutrient concentrations and algae. These are particularly important given that scientists have said the Hudson River Estuary receives the highest rate of nitrogen loading for any estuary in North America. Climate-driven changes could result in nutrient-fueled algal blooms by changing certain estuary dynamics that today function to inhibit algal growth even in our nutrient-overloaded estuary. It will be important for DEC to update its nutrient criteria to set numeric limits – as Riverkeeper has called for since 2019; otherwise, the nutrient data will not necessarily trigger regulatory changes that are needed to reduce pollution. It will also be important to consider the nutrient data relative not only to current conditions, but to future anticipated conditions, given climate warnings from scientists. The DEC anticipates reporting on its results in June 2025.

Disappointingly, however, the DEC’s assessment will not measure bacteria to determine if the Hudson is meeting criteria for safe swimming, kayaking or other recreational uses. DEC had planned to assess a portion of the river for this purpose, but delayed that aspect of the project for at least a year. Riverkeeper will continue to advocate for it.

Hudson River water quality map May 2023This means that Riverkeeper’s ongoing monitoring program, now in its 17th year, will remain the most authoritative source of data about where and when it is safe to swim in the Hudson River. Fecal indicator bacteria are used to determine if untreated sewage or other sources of waste from humans, wildlife or domestic animals are found at concentrations that result in an elevated risk for people who ingest water or immerse themselves during recreation. Many people assume that the government tests the water to gather such fundamental data, but this isn’t true outside of the river’s few public beaches. Overall, our data show that most of the river is safe for swimming most of the time, but water quality is highly variable. Many tributaries, shorelines and areas near Combined Sewer Overflow (CSO) outfalls can remain unsafe for swimming for 2-3 days after rain. Extreme storms may make the entire river temporarily unsafe – a worrying harbinger, given the likelihood that ever more extreme storms will result in more frequent and more intense sewage overflows. Find Riverkeeper’s latest data from our May sampling event with Lamont Doherty Earth Observatory and SeaTow at

The state’s two-year monitoring project will also stop short of assessing the Hudson River along Manhattan’s west side, home of the Hudson River Estuarine Sanctuary, the New York City Triathlon and more. And because the project omits bacterial monitoring, it will not assess the impact of New York City’s 450-plus combined sewer overflow (CSO) outfalls, which discharge upwards of 20 billion gallons of raw sewage and polluted streetwater annually.

The state is now updating Water Quality Standards for bacteria in saline waters around New York City and in the Hudson River up to the Bear Mountain Bridge. The first phase is to update criteria that set different levels of bacteria allowable in waters used for swimming and kayaking. That proposal is open for public comment until June 20. Stay tuned for more information from Riverkeeper on this important issue.

Riverkeeper will also be involved in two other projects taking place this year that will gather data to update state water quality assessments for the Mohawk River and several of its tributaries, and for Peekskill Hollow Brook, a Hudson River tributary that is a source of drinking water for 100,000 people in northern Westchester County. These updates are an important foundation for enforcing the Clean Water Act, now in its 50th year.

In the Mohawk River and 19 of its tributaries, Riverkeeper volunteers, and professors and students from SUNY Cobleskill and SUNY Poly will work with DEC to gather samples at 28 locations in order to complete the state’s first large watershed-scale assessment of fecal indicator bacteria (FIB), an important measure of the Clean Water Act’s “swimmable” goal, showing where water is safe for recreation.

In Peekskill Hollow Brook, Riverkeeper is working with the City of Peekskill with support from DEC’s Hudson River Estuary Program to begin a two-year assessment of water quality that will help inform management of the creek as a drinking water source. The project is a priority of Peekskill’s recently adopted Drinking Water Source Protection Program. Riverkeeper advises the state on the program, and assisted Peekskill in creation of its plan.

Tell Gov. Hochul to block invasive species at the Erie and Champlain canals
Become a Member