Riverine Communities as recognized here following the Cowardin Classification (Cowardin et al. 1979) and include all flowing waters from the mouths of rivers to the springs that serve as their sources and including all first, second, third, and fourth order stream systems. Riverine systems are linear systems. The width along any given stream system spans from shore to shore and includes the intervening stream bottom, stream bed, and aquatic zones. The riverine system is bound on both sides either by the palustrine system or by the upland system. The boundary separating the palustrine and riverine systems is not always sharp. In cases where there are sparsely vegetated shorelines of sand, cobble, or bedrock the riverine system extends to the point along the shoreline where persistent vegetation cover achieves an aerial coverage of 30% or greater. Areas with more than 30% vegetation cover that are still within the flood zone are part of the palustrine system. In some situations the palustrine system extends into the channel of the river. This occurs when there are persistent, emergent wetlands along the shore of the river (rare in Tennessee). Such peristent river marshes are considered part of the palustrine system as is all vegetation shoreward. In such cases, the riverine system is thus limited to the part of the channel that is characterized by submerged, floating, or non-persistent (through winter) emergent vegetation and does not include the persistent, emergent shoreline vegetation.
Tennessee has a wealth of aquatic communities for a land-locked state. Some of the largest rivers in North America run through the state, including the Mississippi, Tennessee, and Cumberland Rivers. Unfortunately, many of Tennessee's rivers have been impacted by damming and channelization. During the early and mid-20th century, many dams were constructed on the Tennessee and Cumberland Rivers and some of their major tributaries by the Tennessee Valley Authority (TVA), permanently altering the natural flow of many streams in Middle and East Tennessee. Such impacts, while beneficial to local economies and industry and important in bringing the U.S. out of the Great Depression, have had devestating effects on aquatic fauna and flora. Such impacts include the extinction of many mussel species and the endangerment of many fish. In West Tennessee most of the major rivers were channelized by the U.S. Army Corps of Engineers for flood-control. These changes in the natural flows of these rivers have permanently impacted their ecology, leading to the deterioration of thousands of acres of wetlands. Many Tennessee streams that haven't been dammed or channelized have been degraded due to both point and non-point source pollution, leading to further degradation of water-quality. In the past few decades, aquatic systems have suffered repeated blows from non-native invasive aquatic species such as Asiatic clam, carp, hydrilla, and water milfoil, and didymo algae. In spite of all the degradation of our waterways many streams do remain in good to excellent shape, especially in more rural parts of Middle and East Tennessee. Several rivers are now protected at the state and federal level as scenic waterways. Tennessee is renowned for its aquatic faunal diversity. The Duck, Clinch, and Powell Rivers are among the biologically richest streams in the temperate portion of the Northern Hemisphere with respect to fish and mussel diversity.