Hudson River Water Quality
Tracking Enterococcus: Monitoring Water Quality at Lamont’s Field Station
At the Hudson River field station, we conduct regular water quality sampling to monitor the presence of Enterococcus bacteria, an indicator species linked with possible water contamination. This research helps us understand what conditions contribute to changes in enterococcus levels, and when waterways might be unsafe for recreational use.
Even when a river appears clear and calm, harmful bacteria can be present. Our testing gives us a science-based look beneath the surface, helping us track patterns in water quality over time and identify when contamination may pose a health risk.
What Is Enterococcus?
Enterococcus is a genus of bacteria that naturally lives in the intestines of humans and animals and is naturally occurring in the environment coming from some animals, plants, and sediments. On its own, it doesn’t always cause illness. But when we detect it in water, it can be a red flag that fecal matter has entered the waterway bringing with it potentially harmful bacteria.
Here's why Enterococcus is so useful in water quality research:
- It is abundant in human sewage, making it easy to detect when contamination occurs. Contamination can come from overwhelmed combined sewage overflow systems after heavy rainstorms or from old leaky pipes and septic systems.
- It is strongly correlated with harmful pathogens, such as noroviruses and bacteria that can cause gastrointestinal illnesses
- It persists in the environment
- It is uncommon in clean, unpolluted water, so its presence is a reliable sign that contamination has occurred
Because of these characteristics, the U.S. Environmental Protection Agency (EPA) often uses Enterococcus as one way to determine whether a marine waterbody is safe for recreational activities like swimming, kayaking, or fishing. Because the Hudson is an estuary its marine connection makes it a good choice for this type of sampling.
How We Test for It
We currently are collecting samples at 4 sites along Piermont Pier to understand spatial distribution and differences in Enterococcus along the Pier.
We use the Enterolert system alongside the IDEXX Quanti-Tray/2000, a method that combines precision with speed. The process works like this:
- A reagent containing a nutrient is added to a 100 mL water sample.
- If Enterococcus is present, it will metabolize the nutrient, causing the sample to fluoresce (glow) under UV light.
- The sample is sealed in a tray with 97 wells and incubated at 41°C for 24 hours.
- Each glowing well indicates a positive result, and the number of positives is used to calculate the Most Probable Number (MPN) of bacteria per 100 mL of water.
This method allows us to detect as few as 1 organism per 100 mL and up to 2,419 organisms, with high confidence in accuracy.
What Do the Results Tell Us?
The EPA has established safety standards to determine whether water is acceptable for recreational use. These standards differ slightly depending on whether the water is freshwater or brackish/saltwater.
Freshwater (north of Bear Mountain Bridge):
- Water is unsafe for this use if a single sample shows more than 61 enterococci per 100 mL. OR if a 5-sample geometric mean is greater than 33/100 mL
Brackish or saltwater (around and south of Bear Mountain Bridge):
- Water is unsafe for this use if a single sample shows more than 104 enterococci per 100 mL. OR if a 5-sample geometric mean is greater than 35/100 mL
If our samples exceed these thresholds, it suggests a heightened risk of illness for anyone recreating in the water.
This Is Just the Beginning
Our weekly sampling efforts offer a snapshot of water quality in a specific place and time and contributes to a much larger set of data that has been accrued over several decades, starting with Lamont research and developing into a Community Science Sampling Program spearheaded by Hudson River Riverkeeper both on the Hudson and in its tributaries. But estuaries are dynamic systems—conditions shift quickly with rainfall, temperature, tides, and human activity.
Testing weekly is a step forward—but it’s not enough to paint the full picture. To learn more, we interviewed our colleague at Riverkeeper.
“We know from our data that there are a lot of times you can get a result that shows the water quality is not safe for swimming that has nothing to do with a pipe break or a sewage discharge from an infrastructure system,” says Dan Shapley, Senior Director of Advocacy at Riverkeeper.
“To meet that vision, we would need to have the government commit to a frequency of sampling that’s way beyond anything that currently exists.”
Our work represents a critical starting point. Every sample collected adds to the growing knowledge we need to protect our waterways—and the people who depend on them.