Louisiana Lake Water Quality

Louisiana lists 785 lakes across 97 counties, 104 of them with a recent water-quality reading. Most of that sampling flows through monitoring run by the Louisiana Department of 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. Most measured Louisiana lakes are productive, often shallow, and frequently algal in late summer; each lake page shows its own phosphorus and chlorophyll-a readings.

By surface area the largest lake here is Toledo Bend Reservoir, at about 165,599 acres, and 156 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. A meaningful share of the state's measured lakes register as hypereutrophic: heavily nutrient-loaded, frequent blooms, low summer transparency. These are usually shallow, surrounded by row-crop agriculture, with little volume to buffer the inputs. The county with the lowest nutrient and algae readings on average is Orleans Parish. The gap between counties is large enough that a single figure for Louisiana lake water quality hides real local variation.