Water Quality

Water of Long Island Sound               Swimming               Rivers, Lakes, and Estuaries               Drinking Water

  The Warming and Rising Waters of Long Island Sound

Annual average bottom and surface water temperature increased over the last 28 years.

The average bottom and surface temperature of the water in Long Island Sound has been rising, with the average bottom temperature rising slightly faster than the surface water.

Earth Day Retrospective: In 2019, the average annual surface water temperature for the Sound was below the average for the previous 28 years; however, the trend indicates an increase of approximately seven percent over that same period. In contrast, the average annual bottom water temperature for the Sound was above the average for the previous 28 years and the trend indicates an increase of approximately 13 percent over that same period.

Earth Day Retrospective: The trend for mean high water data from 2000 to the present for the monitoring station in New Haven, Connecticut indicates an increase of approximately 18 percent over the prior 20-year period.

The Connecticut Institute for Resilience and Climate Adaptation (CIRCA) at the University of Connecticut recommended planning for a sea level rise of 0.5 m (1 foot 8 inches) higher than the national tidal datum in Long Island Sound by 2050. As the Sound rises, more tidal wetlands will be flooded. The natural "migration" of wetlands landward in response to sea level rise is prevented in many places by fill and development. In addition, shore birds that nest in coastal areas, such as the piping plover, will likely be displaced.

_{Technical Note: : Year to year variations in water temperature and water levels in the Sound are less important than trends. There is no "goal" for coastal sea level, but the "Quick Summary" box above presumes warming temperatures and sea level rise are not desired trends.}