Cleaner Lakes Than Petit Lac Saint-Mathieu

Reading the cohort

4 cleaner lakes sit within 30 miles of Petit Lac Saint-Mathieu in the EPA water-quality dataset. With that many higher-grade neighbors close by, Petit Lac Saint-Mathieu's Grade B reflects something specific to the lake itself — not a regional water-quality ceiling. The neighbor list below isn't a small set of marginal upgrades; it's a real cohort of meaningfully cleaner choices for the same Québec weekend.

The nearest cleaner alternative — Lac Ferré in Rimouski-Neigette County — sits 24.5 miles from Petit Lac Saint-Mathieu, putting it firmly in "destination trip" rather than "neighborhood swap" range. The water-quality gap has to be the deciding factor; for a casual outing, Petit Lac Saint-Mathieu is the practical choice and the cleaner options are reserved for purpose-specific visits.

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.