Mesotrophic Lakes in Montana

32 mesotrophic lakes in Montana. Moderate nutrients, good water quality.

Mesotrophic lakes are the productive middle of the trophic scale — TSI between 40 and 50. Clear enough to be inviting, productive enough to support a strong fishery, with moderate phosphorus and a modest algal community that does not dominate the optical signal. 32 lakes in {{stateName}} sit in the mesotrophic band. About 0% are deep (50+ ft); the rest are shallower basins where watershed management keeps nutrients from pushing the system into eutrophy.

Mesotrophic lakes tend to grade B or C on the LakeGrade rubric — the productive-but-clear band lines up with the middle of the letter grades.

#	Lake	County	Grade	Clarity	Depth	TSI
1	Foys Lake	Flathead	A	-	-	44
2	Beaver Lake	Flathead	A	-	-	45
3	Jette Lake	Lake	A	-	-	45
4	Mary Ronan Lake East	Lake	A	-	-	44
5	Lake Five	Flathead	A	-	-	41
6	Murray Lake	Flathead	A	-	-	43
7	Echo Lake	Flathead	A	-	-	42
8	Bootjack Lake	Flathead	A	-	-	43
9	Lake Mary Ronan-Cormorants	Lake	A	-	-	41
10	Inez_deep Lake	Missoula	A	-	-	44
11	Elbow Lake	Powell	A	-	-	41
12	Swan Lake North Basin	Lake	A	-	-	42
13	Nla Lake	Beaverhead	A	13.1 ft	-	43
14	Cooney Reservoir	Carbon	A	12.5 ft	-	43
15	Seeley Lake South Basin	Missoula	A	14.4 ft	-	42
16	Cooney Reservoir	Carbon	B	9.3 ft	-	43
17	Nla Lake	Phillips	B	6.4 ft	-	46
18	Nla Lake	Carter	B	-	-	48
19	Flathead Lake	Lake	B	11.8 ft	-	42
20	Lost Coon Lake	Flathead	B	11.8 ft	-	42
21	Cooney Reservoir	Carbon	B	8.1 ft	-	46
22	Hauser Lake	Lewis and Clark	B	12.7 ft	-	40
23	Island Park Reservoir	Broadwater	B	-	-	49
24	Lake Mcdonald	Flathead	B	-	-	42
25	Lake Mcdonald	Flathead	B	-	-	42
26	Canyon Ferry Lake	Lewis and Clark	B	-	-	48
27	Deep Mill Lake	Yellowstone	B	-	-	47
28	Nla Lake	Pondera	B	3.9 ft	-	50
29	Nla Lake	Valley	B	7.1 ft	-	49
30	Canyon Ferry Lake	Lewis and Clark	B	11.5 ft	-	49
31	Clark Canyon Reservoir	Beaverhead	C	7.4 ft	-	50
32	Hauser Lake	Lewis and Clark	C	8.7 ft	-	46

All mesotrophic 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 →All Montana lakes →

Source: EPA National Aquatic Resource Surveys, 2026.