Stream bed communities are those where stream or river channels have beds that are rocky and frequently exposed for significant periods of the year. Often, during dry periods, flows will diminish and the stream bed consists of an alternating series of rocky bedrock, rubble, or unconsolidated deposits with numerous shallow pools. Some stream bed systems of higher elevations in the mountains may be very rocky and flow may be restricted to areas between boulders or cobble or may flow beneath the rubble altogether in some examples of streams in karst landscapes. Stream beds communities of Tennessee are grouped, following the Cowardin et al. (1979) classification, into bedrock streambeds and rubble (cobble, boulder) stream beds.