Minnesota Lake Water Quality
Water quality grades for 2,209 monitored lakes across 74 counties.
Minnesota's 2,209 graded lakes draw on monitoring done by the Minnesota Pollution Control Agency and the Minnesota DNR, plus volunteer Citizen Lake Monitoring Network samplers who do the actual Secchi-disk work most years. Around 28% of the state's lakes pull an A — 611 top-tier waters. The B and C brackets together hold most of the rest, with the F bracket capturing 285 stressed lakes mostly in the agricultural south of the state.
Most Minnesota lakes sit in the mesotrophic band — moderate productivity, decent clarity, capable of supporting both warm-water and cool-water fisheries. This is the band where well-managed working lakes tend to land. The cleanest county on average is Cass (grade B); the most-stressed is Benton. The gap between the top and bottom counties is large enough that "Minnesota lake water quality" hides real local variation.
Minnesota Lake Water Quality Dataset (2,209 lakes)
Every graded Minnesota lake in one spreadsheet — overall grade and 0–4 score, water clarity, phosphorus, chlorophyll-a, trophic state index, surface area, and max depth, drawn from the EPA Water Quality Portal and state DNR surveys. Enter your email for the CSV.
Lake Map
Explore Minnesota Lakes
Reservoirs in Minnesota
View all 199 reservoirs →199 of 2,209 Minnesota lakes (9%) are man-made reservoirs in the USACE National Inventory of Dams. 30 carry a High or Significant hazard rating. The oldest matched dam dates to 1864.
EPA-Impaired Lakes in Minnesota
View all 1,511 impaired lakes →1,511 of 2,209 Minnesota lakes (68%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 1,182 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Counties
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity | Max Depth |
|---|---|---|---|---|---|
| 1 | East Fox Lake | Crow Wing | A | 16.1 ft | 65 ft |
| 2 | Deep Portage Lake | Cass | A | 15.4 ft | 105 ft |
| 3 | Little Wabana Lake | Itasca | A | 23.8 ft | 57 ft |
| 4 | Clearwater Lake | Cook | A | 30 ft | 65 ft |
| 5 | Clearwater Lake | Lake | A | 18 ft | 46 ft |
| 6 | Lower Hay Lake | Crow Wing | A | 19 ft | 100 ft |
| 7 | Latoka Lake | Douglas | A | 19 ft | 108 ft |
| 8 | Bad Medicine Lake | Becker | A | 25 ft | 84 ft |
| 9 | Big Sugar Bush Lake | Becker | A | 17 ft | 42 ft |
| 10 | Pelican Lake | Otter Tail | A | 16.1 ft | 55 ft |
| 11 | Fullers Lake: East Basin | Beltrami | A | 15 ft | - |
| 12 | Birch Lake | Wright | A | 15 ft | 52 ft |
| 13 | Birch Lake | Cook | A | 18 ft | 69 ft |
| 14 | Birch Lake | Unknown | A | 15 ft | 34 ft |
| 15 | Round Lake | Aitkin | A | 15.3 ft | 59 ft |
| 16 | Round Lake | Cook | A | 16.5 ft | 45 ft |
| 17 | Round Lake | Beltrami | A | 18 ft | 38 ft |
| 18 | Pike Lake | Cook | A | 17.8 ft | 45 ft |
| 19 | Pike Lake | St. Louis | A | 18 ft | 60 ft |
| 20 | Whitefish Lake | Crow Wing | A | 15.1 ft | 138 ft |
| 21 | Horseshoe Lake | Cass | A | 21 ft | 51 ft |
| 22 | Long Lake | Clearwater | A | 20 ft | 80 ft |
| 23 | Long Lake | Cass | A | 21.5 ft | 115 ft |
| 24 | Long Lake | Beltrami | A | 20 ft | 87 ft |
| 25 | Long Lake | Becker | A | 20 ft | 61 ft |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Lower Sioux Hank Lake | Redwood | F | - |
| 2 | Dune Lake | Beltrami | F | - |
| 3 | Fourth Lake | Chisago | F | - |
| 4 | Gonz Lake | Wright | F | - |
| 5 | Snyder Lake | Hennepin | F | - |
| 6 | East Arctic Lake | Scott | F | - |
| 7 | Tadd Lake | Kandiyohi | F | 1.6 ft |
| 8 | Manomin Lake | Lake | F | 2 ft |
| 9 | South Stanchfield Lake | Isanti | F | 2.5 ft |
| 10 | Kauppi Lake | St. Louis | F | 3 ft |
| 11 | Kansas Lake | Watonwan | F | 1.6 ft |
| 12 | North Stanchfield Lake | Isanti | F | 2.8 ft |
| 13 | Upper Tad Lake | Kandiyohi | F | 1 ft |
| 14 | Gleason Lake | Hennepin | F | 1.7 ft |
| 15 | Mountain Lake | Cottonwood | F | 1.2 ft |
| 16 | Bella Lake | Nobles | F | 1 ft |
| 17 | Beaulieu Lake | Mahnomen | F | 1.3 ft |
| 18 | Olson Lake | Big Stone | F | 0.7 ft |
| 19 | Little Kettle Lake | Carlton | F | 3.3 ft |
| 20 | Grossman Slough Lake | Stevens | F | 2.3 ft |
| 21 | Grey Cloud Slough Lake | Washington | F | 3.3 ft |
| 22 | Mcmahon Lake | Scott | F | 3 ft |
| 23 | Greenleaf Lake | Meeker | F | 2.8 ft |
| 24 | Fisher Lake | Scott | F | 0.7 ft |
| 25 | Marshan Lake | Anoka | F | 1.2 ft |
Source: EPA National Aquatic Resource Surveys, 2026.