Cleaner Lakes Than Mcmahon Lake

Reading the cohort

Within 30 miles of Mcmahon Lake, 5 water bodies score higher than its Grade F on the same EPA water-quality metrics. That density of cleaner options is itself a signal — when several nearby lakes score better on the same indicators, the issues at Mcmahon Lake are typically lake-specific (depth, watershed inflow, stratification pattern) rather than regional. The choice for a swim, paddle, or fishing trip is genuinely between meaningfully different water bodies, not between marginal differences in the same dataset.

The closest cleaner alternative — Crystal Lake in Scott County, Grade C — sits miles from Mcmahon Lake. At that distance, the substitution cost is essentially zero: same drive time, same regional access, demonstrably cleaner water on the EPA indicators. For repeat visitors who care about clarity or phosphorus levels, swapping the routine to Crystal Lake is mostly a habit change rather than a logistics change.

The EPA water-quality grading combines clarity (Secchi depth), phosphorus, and chlorophyll-a measurements from state environmental sampling. A higher letter grade reflects measurably cleaner water on those indicators, not subjective beauty or access quality — a Grade A lake might have worse boat-launch facilities or shoreline access than a Grade C neighbor, so the ranking is one input alongside the rest of trip planning. See the methodology page for the full grading formula.

How this list is built

Every lake on LakeQuality has a calculated grade from EPA Water Quality Portal samples — secchi depth, total phosphorus, and chlorophyll-a measured against Metropolitan Council thresholds. To suggest cleaner alternatives, we filter lakes within 30 miles to those with a strictly higher numeric score, then rank by grade improvement with a small proximity tiebreak. Cross-state and limited-data lakes are excluded so the list stays locally relevant.