Question 1

What is the cleanest lake in Minnesota?

Accepted Answer

East Fox Lake has the highest water quality score in our 2026 Minnesota dataset (grade A), based on combined Secchi clarity, phosphorus, and chlorophyll-a measurements. Cleanliness here means low nutrient load, deep water clarity, and minimal algae — measured directly from EPA and state DNR samples.

Question 2

What is the most polluted lake in Minnesota?

Accepted Answer

Among monitored Minnesota lakes, East Arctic Lake ranks among the most polluted by combined phosphorus and chlorophyll-a load. See our full ranking on the most-polluted-lakes trend page for state-by-state details.

Question 3

Where in Minnesota has the cleanest water?

Accepted Answer

Minnesota's clearest waters are concentrated in the deeper, lower-nutrient lakes of the state's northeast — typically older glacial lakes with rocky basins and forested watersheds. The top 25 above shows the highest-scoring lakes statewide; counties like Cook, Lake, and Itasca (MN) or Vilas, Oneida, and Iron (WI) consistently produce A-grade waters.

Question 4

Are these lakes safe to swim in?

Accepted Answer

A and B grade lakes are typically safe for swimming under normal conditions. Chlorophyll-a below 10 µg/L means low risk of harmful algal blooms. Always check posted advisories before swimming — water quality changes seasonally, especially in late summer when blue-green algae bloom risk peaks.

Question 5

How are these grades calculated?

Accepted Answer

Each lake is scored on three signals: Secchi depth (water clarity in feet), total phosphorus (nutrient load in µg/L), and chlorophyll-a (algae concentration in µg/L). Each gets a 0–100 sub-score relative to Minnesota state norms. The three sub-scores average into the overall score, which maps to an A–F letter grade. Methodology details live on our methodology page.

Question 6

What are the top 5 cleanest lakes in the US?

Accepted Answer

There is no single national ranking of cleanest lakes — each state agency uses different metrics. Crater Lake (Oregon) is widely cited as the clearest US lake, with Secchi depths over 30 m. Lake Tahoe and Lake Superior are also top-tier nationally. Within Minnesota, the lakes ranked above are the top 25 by our standardized 2026 grading.

Rank	Lake	County	Grade	Clarity	Phosphorus	Chlorophyll-a	Area
1	East Fox Lake	Crow Wing	A	16.1 ft	10 µg/L	—	240.88 acres
2	Deep Portage Lake	Cass	A	15.4 ft	10 µg/L	—	129.02 acres
3	Little Wabana Lake	Itasca	A	23.8 ft	6.5 µg/L	—	115.73 acres
4	Clearwater Lake	Cook	A	30 ft	4 µg/L	—	461.73 acres
5	Lower Hay Lake	Crow Wing	A	19 ft	13 µg/L	—	700.21 acres
6	Latoka Lake	Douglas	A	19 ft	11 µg/L	—	766.63 acres
7	Bad Medicine Lake	Becker	A	25 ft	6 µg/L	—	803.03 acres
8	Big Sugar Bush Lake	Becker	A	17 ft	10 µg/L	—	521.51 acres
9	Pelican Lake	Otter Tail	A	16.1 ft	15 µg/L	—	4.0K acres
10	Fullers Lake: East Basin	Beltrami	A	49.2 ft	9.5 µg/L	—	-
11	Birch Lake	Wright	A	15 ft	17 µg/L	—	99.82 acres
12	Birch Lake	Cook	A	18 ft	8 µg/L	—	236.31 acres
13	Round Lake	Cook	A	16.5 ft	8.5 µg/L	—	154.48 acres
14	Round Lake	Beltrami	A	59.1 ft	7 µg/L	—	181.06 acres
15	Pike Lake	Cook	A	17.8 ft	6 µg/L	—	814.43 acres
16	Whitefish Lake	Crow Wing	A	15.1 ft	14 µg/L	—	7.7K acres
17	Long Lake	Clearwater	A	20 ft	7 µg/L	—	158.86 acres
18	Long Lake	Cass	A	21.8 ft	9 µg/L	—	1.0K acres
19	Long Lake	Beltrami	A	20 ft	7 µg/L	—	411.95 acres
20	Long Lake	Becker	A	20 ft	8 µg/L	—	414.51 acres
21	Long Lake	Beltrami	A	45.9 ft	8 µg/L	—	-
22	Long Lake	Itasca	A	16.7 ft	8 µg/L	—	155.28 acres
23	Long Lake	Itasca	A	16.9 ft	10 µg/L	—	134.49 acres
24	Dead Lake	Hubbard	A	16 ft	10 µg/L	—	130.64 acres
25	Unnamed Lake	Otter Tail	A	15.1 ft	9 µg/L	—	1.4K acres

Cleanest Lakes in Minnesota

Frequently Asked Questions

How we rank cleanest lakes