Monday, October 12, 2026
August is National Water Quality Month, and the environmental group Friends of the Bay has been marking the month by monitoring the water in Oyster Bay, Cold Spring Harbor and Mill Neck Creek, as it has since joining an environmental study created eight years ago.
“People should always be concerned about our water quality,” Christine Suter, the nonprofit organization’s executive director, said. Oyster Bay has cleaner water than other bays around Long Island, Suter said, but she emphasized the need “to remain vigilant in how our activities on land are affecting water quality.”
Friends of the Bay, which is based in Oyster Bay, has been monitoring water quality in the three bodies of water since 1998. In addition to it’s own pathogen monitoring network it has also taken part in Save the Sound’s Unified Water Study since it was launched in 2017.
Save the Sound is a nonprofit dedicated to protecting the Long Island Sound and other climate-related issues. The Unified Water Study has two tiers of testing, which takes place twice a month.
“I knew there were some nutrient issues going on in the water,” Amanda Hornung, lead volunteer coordinator for Friends of the Bay, said. “I didn’t realize how much it could be in certain areas, especially with some of the bacteria samples we take.”
Hornung, a 25-year-old resident of Bayville, is working with Friends of the Bay on a $67,000 grant awarded by the Long Island Sound Stewardship Fund grant from New York Community Trust, which supports projects that address pressing challenges and monitor the Sound.
According to Suter, 29 differerent organizations take part in The Unified Water Study, monitoring nearly embayments in New York and Connecticut.
To make the data comparable and consistent, each group uses the same methods and equipment to collect the data. The study is funded by a Long Island Sound Futures Fund grant awarded by the National Fish and Wildlife Foundation.
In Tier 1 testing, volunteers and staff use a water meter, or sonde, to take readings at different depths at 14 sites throughout Oyster Bay, Cold Spring Harbor and Mill Neck Creek. Water temperature; the presence, type and distribution of large plants and algae growing in or adjacent to it; the percentage of dissolved oxygen; and the levels of chlorophyll and salinity are analyzed.
Tier II testing is optional and involves more sophisticated techniques compared to the first tier. Testing is also done with a sonde at nine open-water sites and four streams in the Oyster Bay and Cold Spring Harbor watershed. At the end of Tier II testing, six samples — three filtered and three unfiltered — are sent to the Save the Sound Lab in Larchmont, in Westchester County, for further study.
The samples are analyzed for nitrogen and phosphorus levels, which, if too high, can lead to rapid increases in the population of algae in the water, which creates a colored scum on the surface, known as an algal bloom.
Roger Levine, a volunteer boat driver with Friends of the Bay since 2020, said that, before he got involved, he was unaware of the impact of excessive nitrogen in the water, which can lead to oxygen depletion and “dead zones,” upsetting the natural balance of an aquatic ecosystem. The 66-year-old Oyster Bay resident recalled being on the water, seeing the yards and lawns of nearby houses surrounding it and realizing that “everything that goes on those is coming into the bay.”
Measuring oxygen in the water by using cement-filled crates suspended off local docks is another component of Tier II testing. Dissolved oxygen readings at four locations within Cold Spring and Oyster Bay Harbor as well as Mill Neck Creek are logged every 15 minutes from May through October.
According to Suter, there is a balance between water temperature and dissolved oxygen. “When the temperature outside gets warmer,” she said, “warmer weather and warmer water can’t hold as much.”
The collected data is used to produce Save the Sound’s Long Island Report Card. For the 2024 report, released last October, Mill Neck Creek and Oyster Bay were given a grade of A–. The interior and exterior of Cold Spring Harbor got lower marks, a D+ and a C+, respectively. The report, released every two years, evaluates the water quality in five areas of the sound: the Eastern and Western Narrows and the Eastern, Central and Western Basin.
Suter acknowledged that there is no single explanation for the lower water quality in Cold Spring Harbor, but added that Friends of the Bay was searching for an answer.
“We do have some suspicions about some problematic outfall in the area where there may be excessive nitrogen and bacteria input into the bay,” she said, noting that Cold Spring Harbor has consistently had problems with dissolved oxygen, which she attributed to a combination of poor tidal flushing in the inner bay.
Friends of Bay staff and volunteers agreed on the importance of continuing the testing in the future. Those interested in volunteering or learning more about the organization’s work can go to FriendsOfTheBay.org.
“We’re lucky that we are in one of the cleanest bays in the western Long Island Sound,” Suter said, “But we have to work to keep it that way.”
