The map above illustrates the areas of Long Island Sound that are most frequently affected by hypoxia. The colors on the map represent the percentage of years in which hypoxic conditions have occurred in the bottom waters of Long Island Sound since the LISS Water Quality Monitoring program was instituted in the early 1990s.
Hypoxia is a condition that occurs in bodies of water as dissolved oxygen concentrations decrease to levels where organisms become physically stressed and ultimately cannot survive. Prolonged hypoxic conditions result in severe die-offs of animals that are unable to move out of hypoxic waters, mass migrations of mobile animals, changes in water chemistry and other adverse ecological effects. The Long Island Sound Study defines hypoxia as waters with dissolved oxygen concentrations less than 3 mg/L.
The bottom waters in the westernmost areas of Long Island Sound have experienced hypoxia virtually every year since monitoring began. Another area of regular hypoxic conditions is Smithtown Bay in Long Island (station 15).