The latest Long Island Sound water quality map, from the first week of August, went out yesterday afternoon. The black area in the far western end of the Sound shows where dissolved oxygen concentrations are below 1 milligram per liter. This morning at Execution Rocks, DO was at 0.2 milligrams per liter. (Click on the map to enlarge it.)
According to the Connecticut DEP, 178 square miles have DO concentrations of below 3 milligrams per liter, which means hypoxia is moderate, moderately severe or severe, depending on how low DOs are.
to see the two previous maps for comparison.