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LakeQuality
B

Mahnomen County Lake Quality

Minnesota, 16 lakes, average grade B (Good)

There are 16 graded lakes in Mahnomen County. The mix is varied enough that the county-level average tells you the broad strokes, not the choose-this-cabin specifics. The county-wide average lands at B — solid water quality with most lakes carrying clear summer transparency and low-to-moderate phosphorus.

The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is Bass Lake (A); the most-stressed is Island Lake (F).

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Quick Answers for Mahnomen County

Cleanest lakes in Mahnomen County →Cleanest lakes in Minnesota →Safest swimming lakes in Minnesota →

Planning a trip? Check special fishing regulations for Bass Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Minnesota regulations index.

Fishing in Mahnomen County

Mahnomen County Fishing Guide

Fish species and best-graded lakes in Mahnomen County

DNR Reports (36)

Minnesota DNR LakeFinder resources for lakes in Mahnomen County. browse all reports →

These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).

All Lakes in Mahnomen County

16 lakes · 12 graded, 4 not rated12 graded lakes · 4 not rated, hidden

#LakeGradeClarityPhosphorusAlgaeTrophicMax DepthAccess
1ABass LakeMahnomenA13.1 ft10 µg/L4.9 µg/LNo recent samples26 ft✓ Public
2ANorth Twin LakeMahnomenA8.5 ft17 µg/L5.9 µg/LNo recent samples16 ftCarry-in
3ASouth Twin LakeMahnomenA10.2 ft13.5 µg/L3.1 µg/LNo recent samples29 ft✓ Public
4ALittle Elbow LakeMahnomenA6.9 ft21 µg/L6.2 µg/LNo recent samples18 ftCarry-in
5ASargent LakeMahnomenA8.9 ft16 µg/L6.1 µg/LNo recent samples15 ft✓ Public
6ANorris LakeMahnomenA11.6 ft15 µg/L3.2 µg/LNo recent samplesNo recent samplesNot recorded
7CRoy LakeMahnomenC6 ft24 µg/L13.6 µg/LNo recent samples16 ft✓ Public
8CTulaby LakeMahnomenC7.8 ft23 µg/L10.2 µg/LNo recent samples43 ft✓ Public
9CMccraney LakeMahnomenC12.1 ft19 µg/L10.3 µg/LNo recent samplesNo recent samplesCarry-in
10CSnider LakeMahnomenC8.5 ft21 µg/L9.2 µg/LNo recent samples29 ft✓ Public
11DLone LakeMahnomenD7.1 ft48.5 µg/L24 µg/LNo recent samples22 ft✓ Public
12FIsland LakeMahnomenF4.5 ft30 µg/L34.3 µg/LNo recent samples43 ft✓ Public
NRBig LakeMahnomenNR2.1 ft33 µg/L32.3 µg/LNo recent samplesNo recent samplesCarry-in
NRUnnamed LakeMahnomenNR3.3 ft60 µg/L2.9 µg/LNo recent samplesNo recent samplesCarry-in
NRUnnamed LakeMahnomenNR3.3 ft23 µg/L3.8 µg/LNo recent samplesNo recent samplesNot recorded
NRBeaulieu LakeMahnomenNR1.3 ft90 µg/L55.8 µg/LNo recent samplesNo recent samplesCarry-in

NR = not rated: the monitoring record does not meet the evidence bar for a grade. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.

Lake Match

Which lake suits how you actually use one?

Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.

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Other Counties in Minnesota

Clay County

2 lakes · Avg grade A

Morrison County

16 lakes · Avg grade A

Hubbard County

76 lakes · Avg grade A

Cass County

130 lakes · Avg grade A

Cook County

139 lakes · Avg grade A

Crow Wing County

121 lakes · Avg grade A

See how Mahnomen County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 39 states and 2 Canadian provinces.

Source: EPA National Aquatic Resource Surveys, 2026.