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Atlantic Ocean/Long Island Sound Watershed

A brief overview of this watershed and its water quality is presented below. For more detailed information about the Atlantic Ocean/Long Island Sound Watershed, published NYSDEC reports are also available. General information about watersheds is available at the webpage.

Facts about this Watershed

Map of NYS identifying the Atlantic/Long Island Sound Watershed
Click image to view detailed map of watershed

The Atlantic Ocean/Long Island Sound Watershed drains most of the New York City Metropolitan Area and all of Long Island. Located in the Southeast corner of New York State, the watershed encompasses all marine waters in New York Harbor, Long Island Sound, Block Island Sound, and along the South Shore of Long Island, and the fresh waters that drain into them. The Atlantic Ocean Coastline stretches for 117.5 miles from Rockaway Point at New York Bay to Montauk Point in Eastern Suffolk County.

Location: Southwestern New York State

  • All of Kings (Brooklyn), Queens, Nassau and Suffolk Counties,
  • Much of New York (Manhattan) and Bronx Counties, and
  • Portions of southern Westchester County

Size: 1,650 square miles of land area within New York State.

Rivers and Streams: 522 miles of freshwater rivers and streams. Major tributary watersheds within the larger Atlantic/Long Island Sounds Watershed include:

  • Bronx River (63 river/stream miles) 63 river/stream
  • Mamaroneck River (43 miles)
  • Mianus River (43 miles)
  • Peconic River (29 miles)

Lakes, Ponds and Reservoirs: 132 significant freshwater lakes, ponds, and reservoirs (6,728 acres), including:

  • Kensico Reservoir (2,503 lake/reservoir acres)
  • Lake Ronkonkoma (226 acres)

Estuary Waters: 905,934 acres (1,415 square miles) of marine estuary waters.

Ocean Coastline: 118 miles of Atlantic Ocean Coastline.

How is the Water?

Water Quality in The Atlantic Ocean/Long Island Sound Watershed

In the Atlantic/Long Island Sound Watershed, about 53% of river/stream miles, and 61% of lake, pond and reservoir acres have been assessed (see Assessment Report).

Water quality Pie Chart. Rivers: 17% good, 13% Satisfactory, 30% Poor, 41% unassessed. Lakes: 1% good, 46% satisfactory, 8% poor, 45% unassessed
Good water quality: Fully supports designated activities and uses.
Satisfactory: Fully supports designated activities, but with minor impacts.
Poor (Impaired): does not support designated activities and uses.
Unassessed: Insufficient data available.
Water quality Pie Chart. Estuary waters: 12% good, 52% Satisfactory, 37% Poor, 0% unassessed. Ocean coast: 100% good
Good water quality: Fully supports designated activities and uses.
Satisfactory: Fully supports designated activities, but with minor impacts.
Poor (Impaired): does not support designated activities and uses.
Unassessed: Insufficient data available.

Water quality in the Atlantic Ocean/Long Island Sound Watershed experiences considerable impact and stress from the a variety of sources throughout the densely populated urban area. However in spite of these impacts, the waters of the basin remain a rich and valuable recreational, ecological and economic resource. Primary water quality issues in the watershed include low dissolved oxygen (hypoxia) in Long Island Sound that limits aquatic species including lobster, elevated pathogen levels that result in shellfishing restrictions in some waters, algal weed growth in south shore embayment which discourage recreational uses, a legacy of toxic contamination from industrial and other sources that result in fish consumption advisories, municipal wastewater and combined sewer overflow discharges for New York City and other municipalities and urban/stomwater runoff. A number of watershed-based Estuary Management Programs which involve stakeholders from throughout the watershed have been established to manage actions to address these issues. These efforts include the Long Island Sound Study, the New York-New Jersey Harbor Estuary Program, the Peconic Estuary Program and the South Shore Estuary Reserve.

Major water quality concerns in the watershed are:

  • Long Island Sound Hypoxia Impacts on the aquatic ecosystem
  • Shellfishing Restrictions due to elevated pathogen contamination
  • Municipal Wastewater and Combined Sewer Overflow Impacts in New York City and other urban areas
  • Urban/Stormwater Runoff and Industrial Impacts in the densely populated watershed
  • Impacts from Legacy Industrial Toxics Discharges to area Impacts from Legacy Industrial PCB Discharges to Upper Hudson currently being remediated waters
  • Various Other Nonpoint Sources of nutrients and various other pollutants

About Water Quality in New York State

Water chemistry sampling in a NYS stream
Water Chemistry Sampling

Each waterbody in NYS has been assigned a classification, which reflects the designated "best uses" of the waterbody. These best uses typically include the ability to support fish and aquatic wildlife, recreational uses (fishing, boating) and, for some waters, public bathing, drinking water use or shellfishing. Water quality is considered to be good if the waters support their best uses. NYSDEC routinely monitors and assesses water quality throughout the state and publishes detailed reports of these findings. For more information on these monitoring and assessment programs, see Water Quality Monitoring, Assessment and Planning.

What You Can Do!

Each of us lives in a watershed. On our Watershed Stewardship page are some tips on actions that you and your friends can take to help your watershed.

Biological kick sampling in a NYS stream
Biological Kick Sampling

Published Water Quality Monitoring and Assessment Reports

Watershed Management Plan

More about Atlantic Ocean/Long Island Sound Watershed: