Streams, rivers, wetlands and lakes are home for many small animals called macroinvertebrates. These animals generally include insects, crustaceans, molluscs, arachnids and annelids. The term macroinvertebrate describes those animals that have no backbone and can be seen with the naked eye. Some aquatic macroinvertebrates can be quite large, such as freshwater crayfish, however, most are very small. Invertebrates that are retained on a 0.25mm mesh net are generally termed macroinvertebrates. These animals live in the water for all or part of their lives, so their survival is related to the water quality.