Texas Lake Water Quality

Texas lists 1,376 lakes across 221 counties, 84 of which carry a grade. Most of the input behind those grades flows through monitoring run by the Texas Commission on Environmental Quality, 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. A-grade lakes are scarce among the Texas lakes that carry a letter: about 8% of them. Most sit in C or D, productive, often shallow, frequently algal in late summer.

By surface area the largest lake here is Toledo Bend Reservoir Southwest of Haddens, at about 182,490 acres, and 201 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 Hutchinson (grade A); the most-stressed is Dallas. The gap between the top and bottom counties is large enough that a single figure for Texas lake water quality hides real local variation.