Hellbenders - a species of large salamander with an evocative name - can tell us something about the health of a river. Macroinvertebrates are good indicators of water health across the state. Insects, crustaceans, molluscs, and arachnids can all tolerate water quality in different degrees. Mayflies, caddisflies, stoneflies, hellgrammites are all highly sensitive to pollution. Their presence anywhere indicates good water quality. Dragonflies, damselflies, crayfish and clams are somewhat tolerant of pollution. Black fly larvae, lunged snails, and leeches are all pollution-tolerant.