Grade F Lakes, Very Poor

310 lakes (8% of all graded lakes)

Grade F is the bottom of the rubric: clarity often under 3 feet, very high phosphorus, dense algal communities, frequent harmful-algal-bloom risk. 310 lakes (8% of the dataset) end up here.

A large share of the bracket reads as hypereutrophic — heavy nutrient loading, persistent blooms, low summer transparency. These conditions are usually structural rather than transient. Almost none of the F-grade bracket is deep — 4% of lakes here break 50 feet. The combination of shallow basin plus high nutrient input is what produces an F.

A B C D F

310

Total Lakes

281

Minnesota

Wisconsin

Lake	County	State	Clarity	Depth	Fish
Washington Lake	Le Sueur	MN	4.5 ft	51 ft	18
Emily Lake	Le Sueur	MN	2 ft	37 ft	14
Emily Lake	Chisago	MN	1.6 ft	-	0
Wallmark Lake	Chisago	MN	1.6 ft	-	0
Preston Lake	Renville	MN	5 ft	11 ft	13
Budd Lake	Martin	MN	2.6 ft	23 ft	20
Kabetogama Lake	St. Louis	MN	2.6 ft	80 ft	16
North Long Lake	Ramsey	MN	2.5 ft	-	0
Mud Lake	Hennepin	MN	0.9 ft	-	0
Mud Lake	Hennepin	MN	3 ft	-	0
Mud Lake	Otter Tail	MN	1.6 ft	-	0
Mud Lake	Stearns	MN	3 ft	20 ft	16
Snelling Lake	Hennepin	MN	1.6 ft	9.5 ft	10
Pike Lake	Scott	MN	2 ft	9 ft	0
Pike Lake	Ramsey	MN	2.3 ft	16 ft	13
Horseshoe Lake	Rice	MN	2 ft	26 ft	13
Long Lake	Cottonwood	MN	1 ft	-	0
Unnamed Lake	Ramsey	MN	1 ft	-	0
Unnamed Lake	Meeker	MN	0.7 ft	15 ft	10
Unnamed Lake	Benton	MN	1.5 ft	-	0
Unnamed Lake	Becker	MN	1.2 ft	-	0
Unnamed Lake	Pope	MN	3 ft	-	0
Unnamed Lake	Douglas	MN	3.3 ft	-	0
Unnamed Lake	Otter Tail	MN	1.3 ft	-	0
Unnamed Lake	Becker	MN	2.4 ft	76 ft	17
Unnamed Lake	Big Stone	MN	2 ft	15 ft	8
Unnamed Lake	Stevens	MN	1.1 ft	-	0
Unnamed Lake	Swift	MN	0.7 ft	-	0
Unnamed Lake	Wright	MN	1.6 ft	-	0
Unnamed Lake	Watonwan	MN	1 ft	-	0
Unnamed Lake	Itasca	MN	3.3 ft	-	0
Unnamed Lake	Grant	MN	0.7 ft	-	0
Unnamed Lake	Hennepin	MN	-	-	0
Jonathan Lake	Carver	MN	1.5 ft	-	3
Peltier Lake	Anoka	MN	2 ft	18 ft	16
Tetonka Lake	Le Sueur	MN	3 ft	35 ft	19
Wakanda Lake	Kandiyohi	MN	0.5 ft	-	0
Saint Johns Lake	Kandiyohi	MN	0.5 ft	-	0
Clear Lake	Meeker	MN	2.5 ft	18 ft	13
Clear Lake	Brown	MN	0.8 ft	8 ft	12
Clear Lake	Waseca	MN	2.5 ft	34 ft	12
Clear Lake	Stevens	MN	0.7 ft	-	0
Eagle Lake	Carver	MN	2.3 ft	14 ft	8
Eagle Lake	Blue Earth	MN	1 ft	9 ft	0
Ballantyne Lake	Blue Earth	MN	2.5 ft	58 ft	16
Fish Lake	Kanabec	MN	2 ft	8 ft	21
Fish Lake	Becker	MN	1 ft	-	0
Sand Lake	Stearns	MN	2.5 ft	15 ft	0
Hook Lake	McLeod	MN	3 ft	18 ft	3
Wheeler North Lake	Kandiyohi	MN	1 ft	-	0
Venus Lake	Douglas	MN	2.6 ft	-	0
Allie Lake	Renville	MN	2 ft	12 ft	13
Shell Lake	St. Louis	MN	3 ft	15 ft	8
Roberds Lake	Rice	MN	2 ft	43 ft	18
Charlotte Lake	Stevens	MN	0.9 ft	20 ft	10
Island Lake	Lyon	MN	2 ft	8 ft	6
Cedar Lake	Scott	MN	3.1 ft	13 ft	10
Emily Lake	Pope	MN	2 ft	6 ft	26
Wing Lake	Hennepin	MN	2.1 ft	-	0
Rice Lake	Hennepin	MN	2 ft	11.5 ft	16
Rice Lake	Anoka	MN	2.3 ft	-	0
Rice Lake	Morrison	MN	2 ft	8 ft	0
Thompson Lake	St. Louis	MN	3 ft	9 ft	8
Thompson Lake	Dakota	MN	2.8 ft	8 ft	0
Pokegama Lake	Pine	MN	2 ft	25 ft	23
George Lake	Martin	MN	1.6 ft	11 ft	15
George Lake	Blue Earth	MN	2.5 ft	28 ft	9
Jefferson Lake	Le Sueur	MN	2 ft	-	0
Upper Orono Lake	Sherburne	MN	3 ft	-	0
Rhine Lake	Pine	MN	2.5 ft	8 ft	9
Lawrence Lake	Houston	MN	2.3 ft	-	0
Ox Yoke Lake	Hennepin	MN	2.6 ft	-	0
Silver Lake	Olmsted	MN	2 ft	11 ft	13
Silver Lake	Mille Lacs	MN	1 ft	-	10
Big Woods Lake	Carver	MN	1 ft	-	3
Goose Lake	Ramsey	MN	0.7 ft	6 ft	0
Goose Lake	Wright	MN	2.5 ft	14 ft	13
Goose Lake	Carver	MN	1 ft	10 ft	12
Goose Lake	Hennepin	MN	0.8 ft	8 ft	2
Typo Lake	Anoka	MN	1 ft	6 ft	13
Laura Lake	Redwood	MN	2 ft	21 ft	13
Powderhorn Lake	Hennepin	MN	1.3 ft	24 ft	6
Hall Lake	Martin	MN	2.6 ft	27 ft	19
Como Lake	Ramsey	MN	2.5 ft	15.5 ft	11
Fountain Lake	Wright	MN	1 ft	10 ft	5
Fountain Lake	Freeborn	MN	1.5 ft	14 ft	17
Crystal Lake	Blue Earth	MN	1.5 ft	8 ft	12
Benton Lake	Carver	MN	0.8 ft	-	0
Foster Lake	Wright	MN	1.6 ft	10 ft	0
Knife Lake	Kanabec	MN	2.3 ft	15 ft	19
Diamond Lake	Hennepin	MN	1.4 ft	8 ft	0
Diamond Lake	Hennepin	MN	-	5.8 ft	7
Mink Lake	Wright	MN	3 ft	39 ft	8
Ardmore Lake	Hennepin	MN	1.6 ft	20 ft	0
Zumwalde Lake	Stearns	MN	2.3 ft	23 ft	18
Stowe Lake	Douglas	MN	2.6 ft	14 ft	14
Oak Lake	Polk	MN	3 ft	-	0
Elk Lake	Sherburne	MN	2 ft	9 ft	17
Krays Lake	Stearns	MN	3 ft	40 ft	15
Rush Lake	Sherburne	MN	2 ft	11 ft	18

Showing 100 of 310 Grade F lakes.

Frequently Asked Questions

How many lakes have a grade of F?

There are 310 Grade F (Very Poor) lakes in Minnesota and Wisconsin, 281 in Minnesota and 29 in Wisconsin. This represents 8% of all graded lakes.

What does a Grade F mean?

Grade F means very poor water quality with less than 3 ft visibility, very high phosphorus and algae. Potential for harmful algae toxins. Do not swim. Fish kills may occur.

Source: EPA National Aquatic Resource Surveys, 2026.