Overall Health Index

The Long Island Sound report card compares 4 indicators (dissolved oxygen, chlorophyll a, water clarity, dissolved organic carbon) to scientifically derived thresholds or goals. These indicators are combined into an Overall Health Index, which is presented as a subregion percent score.

How is it measured?

The overall health index is the average of the four water quality indicators - dissolved oxygen, dissolved organic carbon, chlorophyll a, and water clarity. 

Threshold Levels

Scores Grade
 0% - < 60% F
 60% - < 70% D
 70% - < 80% C
 80% - < 90% B
90% - 100% A

Each grade is then divided into plus and minuses where the 3 lowest scores (eg. 80-82) is a minus and the top 3 scores (eg. 87-89) is a plus. Example: 80-82%=B-, 83-86%=B, 87-89%=B+.