Michigan Lake Water Quality

Michigan lists 3,392 lakes across 83 counties, 182 of which carry a grade. Most of the input behind those grades flows through monitoring run by the Michigan Department of Environment, Great Lakes, and Energy (EGLE), 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. Roughly 59% of the state's graded lakes carry an A, 107 lakes that earn the top bracket on the combined Secchi, phosphorus and chlorophyll-a rubric. That share is high by national standards and reflects the depth and natural clarity of glacial lakes in the region.

By surface area the largest lake here is Houghton Lake, at about 20,070 acres, and 232 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. Mesotrophic is the dominant trophic class among the graded lakes, a workable middle ground between the pristine oligotrophic deep lakes and the algal-pressured eutrophic shallow ones. The cleanest county on average is Dickinson (grade A); the most-stressed is Chippewa. The gap between the top and bottom counties is large enough that a single figure for Michigan lake water quality hides real local variation.