The biennial Long Island Sound Report Card delivered a stamp of approval for more than a decade’s worth of federal and state investment in improvements to sewage treatment facilities in both Connecticut and New York.

Save the Sound staff cautioned that individual beaches and bays face continued challenges (testing monitored “open water” conditions only, according to a press release), that the westernmost portion of the Sound remains stressed, and that climate change and population growth pose challenges requiring additional investment.

The report was released Monday, Sept. 24.

The most positive results were found in the measurement of dissolved oxygen in the Long Island Sound, a barometer for the health of the waterway. Low levels of dissolved oxygen (hypoxia) can lead to fish die-offs, reduced reproduction of marine life, and other adverse conditions. Improvements to sewage treatment plants in the region have reduced the discharge of nitrogen to the Sound from those plants by 58.5% which, in turn, reduces the depletion of oxygen in the waterway and supports marine life.

For the first time the report includes 10 years of data and an assessment of how water quality is trending in each region of the Sound.

Year-to-year (or even multi-year) fluctuations in water quality can be influenced by weather conditions and other factors, so scientists are wary of identifying a trend until numerous years of data from water quality measurements are available. The 2018 report includes evidence that dissolved oxygen levels, the focus of coordinated conservation efforts, have improved over the past 10 years.  

The region where the improvement is the most dramatic is the Eastern Narrows, which spans the entire open coastline of Westchester County, N.Y., to Darien on the north, and the open coastline of Nassau County to Asharoken, N.Y., on the south side of the Sound. This region went from a “D+” in 2008 to a “B-” in 2017, benefitting from both the upgrades made to its local wastewater treatment plants and those made to plants on the East River, which flows into the western end of the Sound.

Water quality in the Sound is now a far cry from conditions in the 1980s, when a steady increase in population and poorly treated sewage led to harbors full of dying fish and shellfish, dirty beaches, and waters almost devoid of oxygen. By 2000, the U.S. Environmental Protection Agency (EPA), the New York State Department of Environmental Conservation (DEC), and the Connecticut Department of Energy and Environmental Protection (DEEP), agreed to make a significant investment in a clean and healthy Sound. More than two billion dollars were invested over the following 16 years to treat nitrogen at dozens of sewage treatment plants that discharge to the Sound — ultimately achieving a 58.5% reduction in the amount of nitrogen entering Long Island Sound from those plants.

“In many respects what we’re seeing is a victory for the tenets of the Clean Water Act, as well as the commitment shown by New York and Connecticut officials, the EPA, and citizens alike,” Tracy Brown, director of Save the Sound, said. “We now have hard evidence that investment in improved technology at treatment plants pays great dividends.

“The most important step now is to recognize that there is more work to be done — both to keep from sliding backwards in the face of climate change and population pressure, but also to move forward so that the most heavily populated areas of the Sound share in the recovery,” Brown added.

The Western Narrows, home to New York City, have remained stalled at an “F” grade (45%) since 2008. The area is densely developed, heavily populated, and has very little exchange with the Atlantic Ocean, so is still suffering from nitrogen pollution stemming from human waste and stormwater runoff. However, even this most challenging part of the Sound showed significant improvements in dissolved organic carbon in the 10-year data, leading to a sense of optimism for scientists involved in the study.  

In addition to dissolved oxygen, the report measured water clarity, chlorophyll a levels, and dissolved organic carbon. Overall, the geographic report card revealed:



  • The Eastern Basin received an A+ (100%). This region’s water quality has been consistently excellent over the past decade.

  • The Central Basin received an A (96%). Conditions have been consistently supportive of marine life over the past decade.

  • The Western Basin received an A- (92%). This region has shown notable improvement in water quality over the last decade, as the summer zone of lowoxygen continues to shrink.

  • The Eastern Narrows received a B- (82%). This region still needs to improve its dissolved oxygen levels; however, overall water quality has improved significantly over the past decade.

  • The Western Narrows received an F (45%). This part of the Sound is still suffering from nitrogen pollution stemming from human waste and stormwaterrunoff; however, significant improvements in the DOC indicator could be a sign of things to come in future Report Cards.


The Long Island Sound Report Card was produced by Save the Sound and published in using 2008-17 data. Science direction was provided by Dr. Jamie Vaudrey and Dr. Jason Krumholz.

Funding was provided by the Long Island Sound Funders Collaborative. Information can be found at lisfc.org.

The report and steps individuals can take to help improve Long Island Sound water quality is available at: www.savethesound.org.

Save the Sound is a bi-state program of the Connecticut Fund for the Environment with a 45-year track record of restoring and protecting the waters and shorelines of the Long Island Sound. It has offices in Mamaroneck, N.Y., and New Haven.