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.
In spite having a wealth of TVA "lakes" Tennessee actually only has two types of natural lakes and both are quite rare across the state. The majority of what people call lakes in Tennessee are actually impoundments or reservoirs (e.g. Kentucky Lake, Nickajack Lake) that formed following the damming of rivers by the TVA. Tennessee's natural lakes fall into two groups, earthquake-created lakes and ox-bow lakes. Reelfoot Lake and Sunk Lake were both created by the earthquakes that struck along the New Madrid Fault in 1811-1812. Ox bow lakes are formed when meandering streams, like the Mississippi River, changes course and abandons its former channel. The resulting isolated depressions that become cut off from the newly formed river channel are called ox-bow lakes. They are very frequent in the floodplain of the Mississippi River and the Hatchie River in West Tennessee.
Most people are familiar with ponds as being a small circular body of water in a cattle pasture or field on a farm. These types of ponds are artificial ponds and were created by the construction of earthen dams that catch surface drainage from surrounding uplands. Tennessee also has a variety of natural ponds as well. You might ask, "just what is a natural pond?" Tennessee's natural ponds form in flood plains of rivers similar to ox-bow lakes (but tend to be smaller) or they may be created by beavers. Other ponds are associated with sinkholes that have become "stopped-up" or drain very infrequently. These "sinkhole ponds" occur in areas underlain by karst limestone and are mostly limited to Middle Tennessee's limestone regions, espcially the Pennyroyal Plain and southern Eastern Highland Rim. Small ponds that occur in depressions not associated with limestone sinks are often termed "depression ponds" or vernal pools. They are mostly rainwater fed and often dry up each year.