Environmental & Coastal Statistics on Long Island (Nassau & Suffolk Counties)

Long Island’s coastal environment is shaped by the Atlantic Ocean, Long Island Sound, Peconic Bay, and an extensive network of estuaries, tidal creeks, marshes, harbors, bays, and inlets. Nassau County and Suffolk County contain hundreds of miles of tidal shoreline, making the waterfront one of the region’s defining natural assets while also exposing many communities to flooding, erosion, water-quality problems, and rising sea levels.

This page provides a regional overview of beach monitoring, coastal water quality, shoreline erosion, storm risk, and sea-level rise using information from the National Oceanic and Atmospheric Administration (NOAA), New York State Department of Environmental Conservation (NYSDEC), U.S. Geological Survey (USGS), FEMA, and county health agencies. Conditions and monitoring programs change over time, so current official advisories should always be checked before visiting beaches, parks, marinas, or other waterfront areas.

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Coastal & Environmental Indicators

Category	Nassau County	Suffolk County	Regional Context
Permitted or monitored bathing beaches	More than 60 permitted beaches	More than 190 bathing beaches monitored	More than 250 regulated or monitored bathing beaches across the two counties
Beach water-quality concerns	Stormwater runoff is a major factor affecting water quality	Stormwater runoff is the predominant bacterial source at many marine and coastal beaches	Advisories and closures can follow heavy rain, runoff, contamination events, or elevated bacteria readings
Representative erosion concern areas	Long Beach barrier island, Atlantic Beach, and inlet-adjacent shorelines	Fire Island, Smith Point, Montauk oceanfront, and bluff areas	Erosion varies greatly by location and can accelerate during major storms
Sea-level rise projection for the 2050s	Part of New York State’s Long Island projection region	Part of New York State’s Long Island projection region	13 to 25 inches above the 1995–2014 baseline, with an 18-inch medium projection
Primary coastal flood exposure	South Shore, barrier islands, and low-lying bayfront communities	South Shore, East End, barrier islands, and low-lying waterfront communities	Flood severity depends on storm track, surge, tide, local elevation, drainage, and shoreline protection

Source framework: Nassau County Department of Health, Suffolk County Department of Health Services, NOAA Tides & Currents, NYSDEC, USGS, and FEMA.

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Water Quality in Bays & Beaches

Beach water quality is monitored throughout the warmer months by county health departments. Nassau County reports more than 60 permitted beaches along the Atlantic Ocean, Long Island Sound, bays, and harbors. Suffolk County monitors more than 190 bathing beaches distributed across the Atlantic Ocean, Long Island Sound, bays, harbors, lakes, and other recreational waters.

Rainfall is one of the most important factors affecting swimming-water quality. Stormwater flowing across roads, parking lots, lawns, and developed areas can carry bacteria and other contaminants into nearby waterways. Nassau County identifies stormwater runoff as a major factor affecting beach water quality, while Suffolk County says stormwater runoff is the predominant source of bacteria-laden water at many marine and coastal beaches.

Water quality problems are not limited to bathing beaches. The Peconic Bay system, Great South Bay, and other enclosed or slow-flushing waters can be affected by nitrogen from septic systems and wastewater, fertilizer runoff, stormwater, and other nutrient sources. Excess nutrients can contribute to harmful algal blooms, reduced dissolved oxygen, fish kills, and other ecological problems.

Conditions can change quickly after heavy rainfall or contamination events. A beach that was open earlier in the week may later be placed under an advisory or temporarily closed, making current county beach-status information more useful than historical closure counts when planning a visit.

Coastal Erosion

Coastal erosion affects both the North and South Shores of Long Island, although shoreline change can differ substantially from one location to another. Storms, wave energy, sediment movement, inlet activity, bluff geology, dune condition, beach nourishment, and human shoreline structures can all influence whether a particular stretch of coast is losing or gaining material.

In Nassau County, vulnerable areas include portions of the barrier island containing Long Beach, Atlantic Beach, and shoreline near tidal inlets. These areas can experience substantial changes during major coastal storms and may periodically undergo beach nourishment or other shoreline-management work.

Suffolk County contains a much larger and more varied shoreline. Fire Island, Smith Point County Park, and parts of Montauk are among the best-known areas where erosion, dune loss, bluff retreat, or storm-driven shoreline change can become significant.

Erosion should not be described as a single Long Island-wide rate. USGS coastal research shows that some sections of shoreline retreat while others remain relatively stable or accumulate sediment. Individual storms can also remove several feet of beach or dune material in a short period even where longer-term shoreline movement has been more gradual.

Hurricane & Storm Risk

Long Island has a long history of damaging coastal storms, including the 1938 Long Island Express, Hurricane Gloria in 1985, Hurricane Irene in 2011, and Superstorm Sandy in 2012. Nor’easters and less powerful tropical systems can also cause flooding, erosion, wind damage, power outages, and transportation disruptions.

Storm surge is particularly important for low-lying coastal communities. Strong onshore winds can push ocean or bay water inland while astronomical tides, wave action, rainfall, and local drainage conditions compound the flooding. The depth and geographic reach of coastal flooding can vary dramatically depending on a storm’s track, intensity, forward speed, tide cycle, and the elevation of individual neighborhoods.

Many communities along the South Shore, particularly barrier islands and low-lying bayfront areas, face substantial coastal flood exposure. Portions of the North Shore and East End can also experience coastal flooding, especially around harbors, tidal creeks, low-elevation roads, and exposed waterfront property.

Sea-Level Rise

Relative sea level has been rising along the New York coast for generations. Long-term NOAA tide-gauge records from the greater New York and Long Island region show a clear upward trend, reflecting both rising ocean levels and regional land movement. Higher baseline water levels allow ordinary high tides and coastal storms to reach farther inland than they once did.

New York State’s updated sea-level projections treat Long Island as a specific coastal region. For the 2050s, the state’s projections range from approximately 13 inches under the low projection to 25 inches under the high projection compared with the 1995–2014 baseline. The medium projection is approximately 18 inches. These figures represent projected regional sea-level conditions rather than an exact prediction for an individual beach, property, or community.

The projections increase later in the century. For the Long Island region, the state’s 2080s projections range from approximately 23 to 48 inches under the low through high scenarios, with a medium projection of about 32 inches. A separate rapid ice-melt scenario reaches substantially higher levels and is intended to represent a lower-probability but more severe possibility.

Sea-level rise does not only affect permanent shoreline position. Higher average water levels can increase the reach of storm surge, make tidal flooding more frequent, place additional stress on salt marshes and other tidal wetlands, increase shoreline erosion in vulnerable locations, and make drainage more difficult in low-lying communities.

How the Information Is Compiled

This regional overview combines several types of public data rather than relying on a single measurement. Beach counts, water-quality monitoring, and swimming advisories are primarily handled by the Nassau and Suffolk county health departments. Coastal erosion information is informed by USGS shoreline research and state and local coastal studies. Historical storm information comes from NOAA and National Hurricane Center records, while FEMA provides flood-risk mapping used by property owners, governments, insurers, and emergency planners.

Sea-level information is based on NOAA tide-gauge observations and New York State’s science-based coastal projections under 6 NYCRR Part 490. The current state projections use a 1995–2014 baseline and provide separate low, low-medium, medium, high-medium, high, and, for some later periods, rapid ice-melt scenarios. Because shoreline conditions and environmental monitoring change over time, figures on this page should be treated as regional reference information rather than a substitute for current site-specific guidance.

Planning note: Before visiting a Long Island beach, marina, waterfront park, or coastal trail, check current weather, surf conditions, beach-water advisories, flood alerts, and local access information. Conditions can change rapidly following storms and heavy rainfall.