Québec Lake Water Quality

Across Québec, 1,018 lakes carry an active water-quality grade spread over 70 counties. The underlying measurements come from le Ministère de l'Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs, alongside federal programs and volunteer monitoring networks. Roughly 59% of the state's graded lakes carry an A — 604 lakes that earn the top bracket on the combined Secchi/phosphorus/chlorophyll-a rubric. That share is high by national standards and reflects the depth and natural clarity of glacial lakes in the region.

Trophically, oligotrophic lakes — cold, clear, low-nutrient — dominate the state's graded inventory. These are the deep glacial basins that buffer against nutrient inputs by sheer volume, and they hold most of Québec's A-grade waters. The cleanest county on average is Joliette (grade A); the most-stressed is Rouville. The gap between the top and bottom counties is large enough that "Québec lake water quality" hides real local variation.