Calculating Water Quality
1. Refer to the weight table and enter the weight factor for each macroinvertebrate in Column C.
2. Multiply the sensitivity rating (Column A) by the weight factor (Column C) for each macroinvertebrate and enter in Column D.
3. Total Column C (weight factors).
4. Total Column D (sensitivity rating x weight factor).
5. Calculate the Stream Pollution Index (SPI) value.
6. Use the Stream Pollution Index value to find the Water Quality Rating.
Stream Pollution Index = Total Column D / Total Column C =
Water Quality Rating =