Tennessee Lake Water Quality

Tennessee lists 277 lakes across 75 counties, 28 of which carry a grade. Most of the input behind those grades flows through monitoring run by the Tennessee Department of Environment and Conservation, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. The remainder are here because they are real named lakes, not because anyone has sampled them recently. Only about 0% of Tennessee's graded lakes pull an A. The smaller, agricultural-watershed lakes that dominate the graded set tend to carry persistent nutrient loads, and 68% of them fall in the D or F brackets.

By surface area the largest lake here is Kentucky Lake, at about 22,907 acres, and 22 of the lakes in this index cover more than 500 acres. Size is worth knowing before you go: a large deep basin buffers nutrient inputs by sheer volume, while a shallow one warms quickly and can turn over its whole water column in a single summer storm. Eutrophic conditions dominate the graded set: nutrient-loaded, productive, with algal pressure that shows up most years in late summer. These lakes tend to be shallow, in agricultural watersheds, and over-warmed by the time July ends. The cleanest county on average is Rhea (grade B); the most-stressed is Stewart. The gap between the top and bottom counties is large enough that a single figure for Tennessee lake water quality hides real local variation.