Benthic macroinvertebrates were collected in the Big Spring Basin, located in northeastern Iowa, from May through October 1988. The purpose of the study was to develop baseline information on the benthic organisms present in the basin. A total of 167 taxa including seven species of leeches, five genera of snails, three genera of clams, one crayfish genus and over 150 taxa of aquatic insects were identified with the majority of the organisms having been reported in Iowa previously. Benthic organisms not usually encountered in Iowa include the planarian, Cura formanii; the isopod, Lirceus; the beedes, Enrxhrus, Hydrophilus, and llybius; the chironomids, Diamesa and Prodiamesa; the mayfly, Stenacron candidum; the damselfly, Archilestes grandis; the dragonfly, Aeshna tuberculifera; the sconefly, Claassenia and the caddisfly, Helicopsyche borealis. The variety and distribution of benthic organisms within the Big Spring Basin reflect the numerous habitats in the various stream segments. Many of the benthic organisms collected, especially chose not reported before, are known to prefer clear, cold water streams such as those found in the Big Spring Basin. The continued existence of this aquatic life is dependent upon, at a minimum, maintaining current water quality conditions in the basin
