Watersheds are also called drainage basins, and everyone lives in one. The water that runs off your yard or driveway, or flows from nearby streams, eventually reaches a specific destination.
The Long Island Sound watershed span six states and even reaches into Canada. Nearly all of Connecticut lies within it, along with parts of New York, Rhode Island, Massachusetts, New Hampshire, and Vermont. Together, nearly nine million people live within the LIS watershed, including more than four million within the coastal boundary.
It’s the area of land that directly borders Long Island Sound. The coastal boundary is a planning line used by states to manage and protect coastal areas. It includes the shoreline and nearby inland places that affect coastal waters.
If you live in the Long Island Sound watershed, your actions can still impact the Sound, even if you’re outside the official coastal boundary.
Everything that happens on land affects the water that drains through it. The way we care for our lawns, the number of farms and factories, and even the amount of forested land all influence the health of Long Island Sound.
Excess nutrients, such as nitrogen and phosphorus, enter the watershed through fertilizers, wastewater, or septic systems. These nutrients can cause algal blooms and lead to low oxygen “dead zones.”
Pollutants, including heavy metals, pesticides, and PFAS, can enter the water if they are disposed of improperly.
Trash and plastics can travel through waterways and end up in Long Island Sound. The closer you live to the coast, the greater your impact on the Sound. But everyone in the watershed, no matter how far inland, plays a role in its health.
The Long Island Sound coastal boundary is based on natural features like climate, land shape, and water flow, along with political boundaries. It is defined differently in Connecticut and New York.
In Connecticut, the boundary follows an ecological zone called the coastal hardwoods. This reflects how far inland coastal conditions (like salt influence and climate) affect plant life.
In New York, the boundary is based more on geology and water movement. It follows the Harbor Hill moraine across Long Island, which separates groundwater that flows north into Long Island Sound. In the western part of the region, the boundary follows major landmarks like the Robert F. Kennedy Bridge and the Hutchinson River Parkway.
The boundary is not fixed. It can change over time based on new science, environmental changes such as sea level rise, and management decisions that support water quality and habitat protection. The coastal boundary was most recently updated in 2025.
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