What are oligotrophic lakes in Minnesota?

232 oligotrophic lakes in Minnesota. Low nutrients, clear water, excellent for swimming.

What does oligotrophic mean?

Low nutrients, clear water, excellent for swimming.

Oligotrophic Lakes in Minnesota

Oligotrophic lakes are the clear, cold, nutrient-poor end of the trophic scale. The Carlson Trophic State Index measures this as TSI below 40 — water transparent enough to see 15+ feet down, total phosphorus under 12 µg/L, chlorophyll-a barely registering. Across Minnesota, 232 lakes register as oligotrophic — 59% of them break 50 feet of depth, which is the structural condition that underwrites the trophic class. Without depth and a low-nutrient watershed, oligotrophy is hard to sustain.

On our A–F scale, oligotrophic lakes almost always pull an A or B — the same low-nutrient conditions that produce the trophic class also produce the high grade.

#	Lake	County	Grade	Clarity	Depth	TSI
1	Rainy Lake	Cass	A	13.9 ft	29 ft	38
2	East Fox Lake	Crow Wing	A	16.4 ft	65 ft	38
3	Deep Portage Lake	Cass	A	15.4 ft	105 ft	36
4	Clearwater Lake	Cook	A	29 ft	65 ft	29
5	Lower Hay Lake	Crow Wing	A	18.5 ft	100 ft	39
6	Latoka Lake	Douglas	A	19 ft	108 ft	37
7	Bad Medicine Lake	Becker	A	25 ft	84 ft	32
8	Big Sugar Bush Lake	Becker	A	16.5 ft	42 ft	38
9	Pelican Lake	Crow Wing	A	14.3 ft	104 ft	39
10	Fullers Lake	Beltrami	A	15 ft	-	38
11	Birch Lake	Cook	A	18 ft	69 ft	35
12	Round Lake	Aitkin	A	14.5 ft	125 ft	39
13	Round Lake	Cook	A	16.5 ft	45 ft	36
14	Round Lake	Beltrami	A	18 ft	38 ft	35
15	Ada Lake	Cass	A	14 ft	60 ft	39
16	Pike Lake	Cook	A	17.4 ft	45 ft	36
17	Long Lake	Clearwater	A	20.5 ft	80 ft	33
18	Long Lake	Cass	A	21.5 ft	115 ft	37
19	Long Lake	Beltrami	A	20 ft	87 ft	34
20	Long Lake	Becker	A	19.5 ft	61 ft	36
21	Long Lake	Beltrami	A	14 ft	-	37
22	Long Lake	Itasca	A	16.7 ft	72 ft	38
23	Long Lake	Itasca	A	16.9 ft	85 ft	37
24	Dead Lake	Hubbard	A	16 ft	34 ft	39
25	Maple Lake	Cass	A	13.3 ft	45 ft	39
26	Maple Lake	Itasca	A	15.3 ft	39 ft	40
27	West Twin Lake	Crow Wing	A	13.3 ft	42 ft	39
28	Shallow Lake	Itasca	A	16.4 ft	85 ft	38
29	Trout Lake	Itasca	A	18 ft	157 ft	30
30	Trout Lake	Cook	A	18.4 ft	77 ft	35
31	Deer Lake	Itasca	A	13.1 ft	121 ft	39
32	Cowdry Lake	Douglas	A	17.1 ft	52 ft	40
33	Ossawinnamakee Lake	Crow Wing	A	20 ft	63 ft	35
34	Clear Lake	Crow Wing	A	18 ft	63 ft	36
35	Clear Lake	Itasca	A	14.9 ft	30 ft	40
36	Spectacle Lake	Isanti	A	13.8 ft	51.5 ft	39
37	Bear Lake	Lake	A	17.4 ft	31 ft	38
38	Blue Lake	Hubbard	A	17.3 ft	84 ft	36
39	Eagle Lake	Otter Tail	A	22.6 ft	46 ft	32
40	West Fox Lake	Crow Wing	A	15 ft	55 ft	39
41	Star Lake	Crow Wing	A	19 ft	83 ft	37
42	Fish Lake	Otter Tail	A	18 ft	69 ft	38
43	Benedict Lake	Hubbard	A	11.5 ft	91 ft	39
44	Square Lake	Washington	A	17 ft	68 ft	38
45	Shell Lake	Beltrami	A	13 ft	-	39
46	Woman Lake	Cass	A	15 ft	-	40
47	Green Lake	Beltrami	A	18.5 ft	-	34
48	Girl Lake	Cass	A	17.6 ft	81 ft	39
49	Mow Lake	Hubbard	A	14.5 ft	34 ft	39
50	Charlotte Lake	Wright	A	17.1 ft	46 ft	39
51	Big Mcdonald Lake	Otter Tail	A	17.4 ft	46 ft	39
52	Bass Lake	Otter Tail	A	17.4 ft	-	39
53	Bass Lake	Crow Wing	A	16.1 ft	47 ft	38
54	Bass Lake	Itasca	A	18.2 ft	65 ft	36
55	Island Lake	St. Louis	A	14.5 ft	65 ft	38
56	Island Lake	Crow Wing	A	15.1 ft	76 ft	39
57	Island Lake	Cass	A	17.5 ft	40 ft	37
58	Island Lake	Beltrami	A	16 ft	-	38
59	Island Lake	Hubbard	A	16.4 ft	32 ft	39
60	Moose Lake	Beltrami	A	15.1 ft	71 ft	38
61	Crooked Lake	Hubbard	A	19 ft	-	36
62	Crooked Lake	Crow Wing	A	15 ft	54 ft	39
63	Cedar Lake	Morrison	A	16.2 ft	88 ft	37
64	Big Pine Lake	Aitkin	A	17 ft	78 ft	38
65	Lizzie Lake	Otter Tail	A	16.4 ft	66 ft	39
66	Turtle Lake	Becker	A	23 ft	73 ft	34
67	Turtle Lake	Itasca	A	17.1 ft	54 ft	36
68	Lower Bottle Lake	Hubbard	A	15 ft	110 ft	38
69	Pokegama Lake	Itasca	A	16.1 ft	112 ft	39
70	Sandy Lake	Beltrami	A	16 ft	-	37
71	Pickerel Lake	Becker	A	18 ft	74 ft	37
72	Strawberry Lake	Becker	A	17.5 ft	40 ft	34
73	Gull Lake	Cook	A	15.5 ft	-	37
74	Henderson Lake	Kandiyohi	A	13.5 ft	57 ft	38
75	Upper Birch Lake	Isanti	A	10.8 ft	-	39
76	Upper Bottle Lake	Hubbard	A	16 ft	55 ft	39
77	Courthouse Lake	Carver	A	18.9 ft	57 ft	39
78	Silver Lake	St. Louis	A	19.3 ft	29 ft	39
79	Heart Lake	Beltrami	A	14.5 ft	-	39
80	West Battle Lake	Otter Tail	A	18 ft	108 ft	37
81	Wabana Lake	Itasca	A	18 ft	115 ft	36
82	Roy Lake	Crow Wing	A	11.7 ft	26 ft	40
83	Little Mantrap Lake	Hubbard	A	17 ft	54 ft	37
84	Clitherall Lake	Otter Tail	A	14.1 ft	69 ft	40
85	Kimball Lake	Crow Wing	A	18.4 ft	77 ft	36
86	Baby Lake	Cass	A	12.5 ft	69 ft	40
87	Crystal Lake	Cass	A	16 ft	40 ft	36
88	West Sylvia Lake	Wright	A	22 ft	97 ft	34
89	Serpent Lake	Crow Wing	A	25 ft	65 ft	35
90	North Twin Lake	Beltrami	A	17.4 ft	59 ft	36
91	Stuart Lake	Otter Tail	A	17.5 ft	49 ft	40
92	North Star Lake	Itasca	A	19 ft	90 ft	36
93	Pleasant Lake	Cass	A	15.5 ft	72 ft	39
94	Little Bass Lake	Beltrami	A	16 ft	22 ft	38
95	Pulaski Lake	Wright	A	18 ft	-	38
96	Little Mcdonald Lake	Otter Tail	A	26.5 ft	109 ft	33
97	Bay Lake	Crow Wing	A	18.5 ft	74 ft	36
98	Webb Lake	Cass	A	18 ft	84 ft	38
99	Little Hubert Lake	Crow Wing	A	18 ft	41 ft	39
100	Big Trout Lake	Crow Wing	A	16.9 ft	128 ft	37

All oligotrophic lakes →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 →Montana 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 Minnesota lakes →

Source: EPA National Aquatic Resource Surveys, 2026.