Hypereutrophic Lakes in Oregon

14 hypereutrophic lakes in Oregon. Very high nutrients, dense algae, poor clarity.

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. 14 hypereutrophic lakes are on the {{stateName}} books. Almost none of them are deep — 0% break 50 feet. Shallow basin plus heavy nutrient input is the consistent recipe.

Hypereutrophic lakes overwhelmingly grade D or F — the trophic class and the grade are measuring closely-related dimensions of the same underlying nutrient regime.

#	Lake	County	Grade	Clarity	Depth	TSI
1	Williamson River Outlet Lake	Klamath	F	-	-	75
2	Malheur Lake	Harney	F	-	-	84
3	Mid-Trench Lake	Klamath	F	-	-	78
4	Fremont Bridge Lake	Klamath	F	-	-	81
5	Agency Lake South	Klamath	F	-	-	71
6	Shoalwater Bay Lake	Klamath	F	-	-	81
7	Upper Klamath Lake	Klamath	F	-	-	79
8	Rattlesnake Point Lake	Klamath	F	-	-	79
9	Mid-North Lake	Klamath	F	-	-	76
10	Lake Billy Chinook	Jefferson	F	-	-	71
11	Brownlee Reservoir	Baker	F	-	-	82
12	Lake Billy Chinook	Jefferson	F	-	-	75
13	Cold Springs Reservoir	Umatilla	F	-	-	78
14	Upper Klamath Lake	Klamath	F	-	-	72

All hypereutrophic 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 →Arkansas version →Oklahoma version →Kansas version →Nebraska version →Nevada version →Arizona version →Idaho version →Montana version →New Mexico version →All Oregon lakes →

Source: EPA National Aquatic Resource Surveys, 2026.