Eutrophic Lakes in Montana
2 eutrophic lakes in Montana. High nutrients, frequent algae, reduced clarity.
Eutrophic lakes — TSI 50 to 70 — are nutrient-rich and productive, with persistent summer algal communities that drive visible reductions in clarity. These conditions are not failures; they reflect a lake doing what nutrient-loaded waters do. 2 Montana lakes register as eutrophic. Only 0% are deep — eutrophy correlates with shallowness, agricultural watersheds, and the kind of nutrient-input history that takes decades to shift.
Eutrophic lakes typically grade C or D on our A–F scale. The same nutrient richness that defines the trophic class drives the lower grade.
| # | Lake | County | Grade | Clarity | Depth | TSI |
|---|---|---|---|---|---|---|
| 1 | Canyon Ferry Lake | Broadwater | C | 8.9 ft | - | 50 |
| 2 | Bighorn Lake | Big Horn | C | - | - | 57 |
All eutrophic lakes →Minnesota version →Wisconsin version →Illinois version →Michigan version →Iowa version →Ohio version →Pennsylvania version →New York version →Missouri version →Indiana version →North Dakota version →South Dakota version →Florida version →Colorado version →North Carolina version →Vermont version →Texas version →Oregon version →Arkansas version →Oklahoma version →Kansas version →Nebraska version →Nevada version →Arizona version →Idaho version →New Mexico version →Tennessee version →Alabama version →Virginia version →Kentucky version →Utah version →Washington version →Wyoming version →Georgia version →Massachusetts version →Ontario version →Québec version →Nova Scotia version →British Columbia version →Newfoundland and Labrador version →All Montana lakes →
Source: EPA National Aquatic Resource Surveys, 2026.