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I I I I I I I I I I I I I I I I I I I Benthic macro invertebrates were sampled because many are sensitive to physical and chemical changes in their habitat; many live in the water over a year; they cannot easily ~scape pollution as some fish can; and they are easily collected in streams and rivers (Mitchell and Stapp 1990). There are multiple factors which determine why certain organisms live within a stream, including water temperature patterns, discharge patterns, . substrates and trophic relationships (Mitchell and Stapp 1990). The relationship between the composition of the benthic macro invertebrate community and water quality has been recognized and documented (Mitchell and Stapp 1990). Benthic macro invertebrates can be used as pollution indicator organisms because each organism can only live within certain physical and chemical environments. Some organisms survive in many types of environments, and therefore are pollution tolerant. Other organisms are extremely sensitive to pollution. If the stream environment is altered because of a change in water quality, these organisms will no longer be present. Benthic macroinvertebrates can be characterized into three groups: pollution-intolerant, wide range, and pollution-tolerant. Organisms within the pollution-intolerant category cannot live with changes in water quality. Presence of these organisms generally indicates good water quality. These organisms include: Dobsonfly larva, Stonefly nymph, Caddisfly larva, snails, Riffle Beetle adult, Water Penny, and Mayfly nymph. Organisms within the wide range category tolerate a variety of water quality conditions and include: Scud, Dragonfly nymph, Clam, Crane Fly larva, Crayfish, Damselfly larva, Sowbug, and Beetle larva. Organisms highly tolerant of pollution include: Aquatic Worms, Pouch Snails, Leeches, Midge larva, and Black Fly larva. Dominance by these organisms indicates poor water quality (Mitchell and Stapp 1990). Many of the organisms detailed in Table 3 are not frequently used as indicator species and it is not prudent to draw conclusions because of their existence in Trott 9