This document discusses how different levels of pollution affect macroinvertebrate species in streams and ponds. Streams with no pollution will contain a variety of macroinvertebrate animals, while more polluted streams will have fewer species. The type and number of macroinvertebrate species can indicate the water quality, with pollution-sensitive species only existing in clean water. Higher pollution levels eliminate some species and allow more pollution-tolerant species to dominate. Common human causes of stream pollution mentioned are littering, chemical runoff, and physical alterations like piped or straightened streams.