A
B
C
D
Sensitivity
Macroinvertebrate
Sensitivity Rating
Abundance
Weight Factor
A x C
Very Sensitive
Stonefly nymph
10
Mayfly nymph
9
Sensitive
Alderfly larva
8
Caddisfly larva
Water mite
6
Tolerant
Dragonfly nymph
4
Waterstrider
Whirligig beetle & larva
Damselfly nymph
3
Freshwater shrimp
Very Tolerant
Diving beetle
2
Freshwater worm
Waterboatman
Backswimmer
Bloodworm
1
TOTAL
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.