Hypereutrophic Lakes
Very high nutrients, dense algae, poor clarity. 100 lakes (2% of all measured lakes).
Hypereutrophic lakes (TSI above 70) are at the upper end of the productivity scale: visible algal blooms most weeks of summer, clarity often under 3 feet, and meaningful risk of harmful-algal-bloom toxin events. 100 hypereutrophic lakes are on the the United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs. LakeQuality covers books. Almost none of them are deep — 3% break 50 feet. Shallow basin plus heavy nutrient input is the consistent recipe.
Hypereutrophic lakes carry the highest phosphorus and chlorophyll-a readings on record; the trophic class and the readings are measuring closely related dimensions of the same underlying nutrient regime.
Hypereutrophic Lakes by State
Frequently Asked Questions
What is an hypereutrophic lake?
Very high nutrients, dense algae, poor clarity. There are 100 hypereutrophic lakes across the United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs. LakeQuality covers, representing 2% of all measured lakes.
Can you swim in hypereutrophic lakes?
Hypereutrophic lakes are generally not safe for swimming due to dense algae, potential toxins, and very poor visibility.
Source: EPA National Aquatic Resource Surveys, 2026.