Overall Health Index

The Long Island Sound report card compares 4 indicators (dissolved oxygen, nutrients, chlorophyll a, water clarity) 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 five water quality indicators - dissolved oxygen, total nitrogen, total phosphorus, chlorophyll a, and water clarity. 

Threshold Levels

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

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+.