| Aquatic Creature | Pollution Tolerance Level* | Number of These Creatures Found in the Stream |
|---|---|---|
| Mayflies (Ephemeroptera) | 1-4 | |
| Stoneflies (Plecoptera) | 0-2 | |
| Caddisflies (Trichoptera) | 0-4 | |
| Diptera (True Flies) | 2-6 | |
| Odonata (Dragonflies & Damselflies) | 1-9 | |
| Megaloptera (Dobsonflies & Alderflies) | 0-4 | |
| Beetles (Coleoptera) | 4-5 | |
| Moths (Lepidoptera) | 5 | |
| Scuds (Amphipoda) | 4-8 | |
| Sowbugs (Isopoda) | 8 | |
| Crayfish (Decapoda) | 6 | |
| Worms (Class Oligochaeta) | 8 | |
| Leeches (Class Hirudinea) | 10 | |
| Snails (Class Gastropoda) | 7 | |
| Clams (Class Pelecypoda) | 7 |
*Tolerance level indicates the level of sensitivity to pollution. It is based on a 0-10 scale. Within that range, 0 is intolerant, and 10 is very tolerant. If you find many intolerant species, the stream is probably very healthy. If you find many tolerant species, the health of the river may be in question. This exercise (with insect picture page) was developed for an ASERP Orientation by Jim Lafley.
U.S. Fish and Wildlife Service