Clean water is critical to the health of Long Island Sound and the people, wildlife, and economies that depend on it. Water quality affects habitat conditions, fisheries, recreation, and public health. Because the Sound is shaped by the 16,000-square-mile watershed that drains into it, improving water quality requires addressing both local and upstream sources of pollution.
Decades of coordinated action by Connecticut, New York, and EPA have significantly reduced nitrogen pollution, a major driver of low oxygen (hypoxia) in Long Island Sound. Following the approval of a nitrogen Total Maximum Daily Load (TMDL) in 2000, both states upgraded wastewater treatment plants and incorporated nitrogen limits into discharge permits. These efforts have removed over 47 million pounds of nitrogen per year from point sources, helping to reduce the size and duration of seasonal hypoxia by more than half compared to pre-2000 conditions.
Despite this progress, challenges remain. Hypoxic zones still occur each summer, and beach closures, shellfish bed closures, and other water quality impairments persist throughout the Sound and its embayments. Pollution from stormwater, groundwater, and other nonpoint sources, as well as toxic contaminants and marine debris, continue to affect the Sound’s waters. Climate change and more frequent extreme weather events may intensify these impacts, particularly in areas with aging infrastructure or poorly planned land use. The objectives under this goal target the key stressors affecting Long Island Sound: excess nutrients, pathogens, toxic contaminants, marine debris, and land-use practices that degrade water quality. Actions from 2025 to 2029 will focus on reducing pollutant inputs, improving watershed management, and building more resilient water infrastructure to support the long-term health of the Sound.
Reduce nutrients across the watershed to restore and protect water quality and mitigate impacts on ecosystem health in LIS and its embayments.
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Improve the ecosystem health of Long Island Sound and its watershed through protection and positive land use practices.
Reduce pathogens and increase monitoring to protect water quality and human health, ensuring safe recreational and commercial use.
Research, monitor, assess, and reduce emerging and legacy toxic contaminants to mitigate impacts on water and habitat quality in LIS.
Achieve trash free waters by increasing clean-up efforts and preventing marine debris from entering LIS.
Making Long Island Sound’s water cleaner by removing excess nutrients such as nitrogen is going to require different solutions. The Nature Conservancy in Connecticut describes many of the choices in its LIS Water Quality website.
Hypoxia, low levels of oxygen, plague coastal waters, including Long Island Sound, every summer. These “dead zones” can force fish and invertebrates to scatter, and make others susceptible to disease. When concentrations are extremely low fish and shellfish unable to flee may die. The video, created by the NOAA Environmental Visualization Lab, describes how high levels of nutrients lead to hypoxia. The setting is the Gulf of Mexico, but much of what is discussed applies to the Sound. The video was produced with support from the Smithsonian Institution, Dalhousie University, and Texas A&M.
Impervious Surface – Any surface in the landscape that cannot effectively absorb or infiltrate rainfall.
Nutrients – Essential elements required by an organism for growth. In a marine context, this term is typically used to refer to nitrogen and phosphorus, but can also include silica (required by diatoms) and micronutrients such as iron, zinc, and magnesium.
Riparian Buffer – The vegetated area adjacent to a river, stream, or other water body.
Runoff – Flows of water into a stream, lake, or estuary; typically, from a rainfall event where rate of accumulation exceeds losses from infiltration and evapo-transpiration.
See more definitions in glossary.
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