Oligotrophic

Oligotrophic Lakes in Minnesota & Wisconsin

Low nutrients, clear water, excellent for swimming. 1,398 lakes (37% of all graded lakes).

An oligotrophic lake is what most people picture when they think of pristine northern lake country: clarity to depth, no algal scum, cold water that holds dissolved oxygen all the way to the bottom even in August. Across Minnesota and Wisconsin, 1,398 lakes register as oligotrophic — 31% 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 the LakeGrade rubric, oligotrophic lakes almost always pull an A or B — the same low-nutrient conditions that produce the trophic class also produce the high grade.

Oligotrophic Mesotrophic Eutrophic Hypereutrophic

Lake	County	State	Grade	Clarity	Depth
East Fox Lake	Crow Wing	MN	A	16.1 ft	65 ft
Deep Portage Lake	Cass	MN	A	15.4 ft	105 ft
Little Wabana Lake	Itasca	MN	A	23.8 ft	57 ft
Clearwater Lake	Cook	MN	A	30 ft	65 ft
Clearwater Lake	Lake	MN	A	18 ft	46 ft
Lower Hay Lake	Crow Wing	MN	A	19 ft	100 ft
Latoka Lake	Douglas	MN	A	19 ft	108 ft
Bad Medicine Lake	Becker	MN	A	25 ft	84 ft
Big Sugar Bush Lake	Becker	MN	A	17 ft	42 ft
Fullers Lake: East Basin	Beltrami	MN	A	49.2 ft	-
Birch Lake	Cook	MN	A	18 ft	69 ft
Birch Lake	Unknown	MN	A	15 ft	34 ft
Round Lake	Aitkin	MN	A	15.3 ft	59 ft
Round Lake	Cook	MN	A	16.5 ft	45 ft
Round Lake	Beltrami	MN	A	59.1 ft	-
Pike Lake	Cook	MN	A	17.8 ft	45 ft
Pike Lake	St. Louis	MN	A	18 ft	60 ft
Horseshoe Lake	Cass	MN	A	21 ft	51 ft
Long Lake	Clearwater	MN	A	20 ft	80 ft
Long Lake	Cass	MN	A	21.8 ft	115 ft
Long Lake	Beltrami	MN	A	20 ft	87 ft
Long Lake	Becker	MN	A	20 ft	61 ft
Long Lake	Cass	MN	A	16.8 ft	37 ft
Long Lake	Beltrami	MN	A	45.9 ft	-
Long Lake	Itasca	MN	A	16.7 ft	72 ft
Long Lake	Itasca	MN	A	16.9 ft	85 ft
Dead Lake	Hubbard	MN	A	16 ft	34 ft
Unnamed Lake	Otter Tail	MN	A	15.1 ft	95 ft
Maple Lake	Itasca	MN	A	15.3 ft	39 ft
West Twin Lake	Crow Wing	MN	A	19.8 ft	-
Sunshine Lake	St. Louis	MN	A	20 ft	37 ft
Shallow Lake	Itasca	MN	A	16.4 ft	85 ft
Trout Lake	Itasca	MN	A	15.5 ft	135 ft
Trout Lake	Itasca	MN	A	18 ft	157 ft
Trout Lake	Cook	MN	A	19 ft	77 ft
Otter Lake	Otter Tail	MN	A	18 ft	64 ft
Eddy Lake	Lake	MN	A	16.5 ft	95 ft
Cowdry Lake	Douglas	MN	A	17 ft	52 ft
Ossawinnamakee Lake	Crow Wing	MN	A	20 ft	63 ft
Clear Lake	Crow Wing	MN	A	18 ft	63 ft
Clear Lake	Aitkin	MN	A	16 ft	24 ft
Clear Lake	Itasca	MN	A	14.9 ft	30 ft
Bear Lake	Lake	MN	A	17.4 ft	31 ft
Emerald Lake	Beltrami	MN	A	31.2 ft	-
Blue Lake	Hubbard	MN	A	17.4 ft	84 ft
Blue Lake	Crow Wing	MN	A	19 ft	48 ft
Eagle Lake	Otter Tail	MN	A	22.6 ft	46 ft
West Fox Lake	Crow Wing	MN	A	15 ft	55 ft
Spearhead Lake	Hubbard	MN	A	15 ft	81 ft
Ida Lake	Douglas	MN	A	16.5 ft	106 ft
Star Lake	Crow Wing	MN	A	19 ft	83 ft
Star Lake	Otter Tail	MN	A	16.7 ft	94 ft
Upper Maple Lake	Wright	MN	A	18 ft	76 ft
Partridge Lake	Crow Wing	MN	A	16.2 ft	42 ft
Fish Lake	Otter Tail	MN	A	17.8 ft	69 ft
Sand Lake	Cass	MN	A	21 ft	54 ft
Jenny Lake	Lake	MN	A	15.5 ft	93 ft
Roger Lake	Crow Wing	MN	A	16 ft	64 ft
Hamlet Lake	Crow Wing	MN	A	18.5 ft	88 ft
Square Lake	Washington	MN	A	17 ft	68 ft
Shell Lake	Beltrami	MN	A	42.7 ft	-
Tofte Lake	Lake	MN	A	18.5 ft	73 ft
Andrusia Lake	Beltrami	MN	A	15.5 ft	60 ft
Green Lake	Beltrami	MN	A	60.7 ft	-
Green Lake	Beltrami	MN	A	39.4 ft	-
Girl Lake	Cass	MN	A	17 ft	81 ft
Charlotte Lake	Wright	MN	A	17.1 ft	46 ft
Big Mcdonald Lake	Otter Tail	MN	A	16.4 ft	46 ft
Bass Lake	Otter Tail	MN	A	16.9 ft	-
Bass Lake	Crow Wing	MN	A	16.1 ft	47 ft
Bass Lake	Itasca	MN	A	18.2 ft	65 ft
Bass Lake	Cass	MN	A	-	55 ft
Island Lake	Cass	MN	A	15 ft	45 ft
Island Lake	Crow Wing	MN	A	15.3 ft	76 ft
Island Lake	Cass	MN	A	17.5 ft	40 ft
Island Lake	Beltrami	MN	A	52.5 ft	-
Island Lake	Hubbard	MN	A	16.4 ft	32 ft
Crooked Lake	Hubbard	MN	A	19.2 ft	-
Crooked Lake	Crow Wing	MN	A	15 ft	54 ft
Portage Lake	Cass	MN	A	22.8 ft	84 ft
Cedar Lake	Morrison	MN	A	16.4 ft	88 ft
Big Pine Lake	Aitkin	MN	A	16.5 ft	78 ft
Lizzie Lake	Otter Tail	MN	A	16.4 ft	66 ft
Eagles Nest Lake	St. Louis	MN	A	15.5 ft	49 ft
Turtle Lake	Becker	MN	A	23 ft	73 ft
Turtle Lake	Itasca	MN	A	17.1 ft	54 ft
Lower Bottle Lake	Hubbard	MN	A	15 ft	110 ft
Pokegama Lake	Itasca	MN	A	16 ft	112 ft
Sandy Lake	Beltrami	MN	A	52.5 ft	-
Pickerel Lake	Becker	MN	A	18 ft	74 ft
Pickerel Lake	Clearwater	MN	A	16.1 ft	60 ft
Strawberry Lake	Becker	MN	A	17.8 ft	40 ft
Middle Cormorant Lake	Becker	MN	A	15.1 ft	40 ft
Mcavity Lake	Itasca	MN	A	17 ft	29 ft
Gull Lake	Cook	MN	A	16.4 ft	-
Upper Bottle Lake	Hubbard	MN	A	16 ft	55 ft
Devil'S Lake	Otter Tail	MN	A	15 ft	67 ft
Hand Lake	Cass	MN	A	17 ft	57 ft
Ox Yoke Lake	Cass	MN	A	17.5 ft	42 ft
Ottertrack Lake	Unknown	MN	A	20.7 ft	116 ft

Showing 100 of 1,398 oligotrophic lakes.

Frequently Asked Questions

What is an oligotrophic lake?

Low nutrients, clear water, excellent for swimming. There are 1,398 oligotrophic lakes in Minnesota and Wisconsin, representing 37% of all graded lakes.

Can you swim in oligotrophic lakes?

Oligotrophic lakes are excellent for swimming, they have crystal clear water with minimal algae and very low nutrient levels.

Source: EPA National Aquatic Resource Surveys, 2026.