Late afternoon sun over Slim Lake, scattering a bright path across wind-textured water

Flathead County Lake Quality

Montana, 108 lakes, average grade B (Good)

Flathead County has 108 monitored lakes, enough that within-county variation matters as much as the county average. Some are deep glacial basins, others are shallow agricultural-watershed waters, and the measurements reflect that mix. 9 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county-wide average lands at B — solid water quality with most lakes carrying clear summer transparency and low-to-moderate phosphorus.

Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Tally Lake (A) is the cleanest in the county.

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Quick Answers for Flathead County

Cleanest lakes in Flathead County →Cleanest lakes in Montana →Safest swimming lakes in Montana →

Planning a trip? Check special fishing regulations for Tally Lake — or check the official Montana fishing regulations.

All Lakes in Flathead County

108 lakes · 9 graded, 99 not rated9 graded lakes · 99 not rated, hidden

Include not-rated lakes (99)

#	Lake	Grade	Clarity	Phosphorus	Algae	Trophic	Access
1	ATally LakeFlathead	A	15.2 ft	4.7 µg/L	0.8 µg/L	No recent samples	Not recorded
2	AWhitefish LakeFlathead	A	22 ft	2.8 µg/L	0.9 µg/L	No recent samples	✓ Public
3	ASmith LakeFlathead	A	No recent samples	7.4 µg/L	0.8 µg/L	No recent samples	Not recorded
4	ALittle Bitterroot Lake CenterFlathead	A	No recent samples	4 µg/L	1 µg/L	No recent samples	Not recorded
5	CMcgilvray LakeFlathead	C	No recent samples	5.9 µg/L	1.7 µg/L	No recent samples	Not recorded
6	CHanson-Doyle LakeFlathead	C	No recent samples	7.3 µg/L	2.3 µg/L	No recent samples	Not recorded
7	CBailey LakeFlathead	C	No recent samples	6.9 µg/L	2 µg/L	No recent samples	Not recorded
8	DFoys LakeFlathead	D	No recent samples	15.8 µg/L	4.1 µg/L	No recent samples	Not recorded
9	DRogers LakeFlathead	D	No recent samples	11.6 µg/L	2.6 µg/L	No recent samples	Not recorded
	NRHalfmoon LakeFlathead	NR	17.8 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRSpencer LakeFlathead	NR	13.5 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRLost Coon LakeFlathead	NR	11.8 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRBailey LakeFlathead	NR	19.5 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRBlanchard LakeFlathead	NR	19 ft	No recent samples	No recent samples	No recent samples	✓ Public
	NREcho LakeFlathead	NR	15.2 ft	No recent samples	No recent samples	No recent samples	✓ Public
	NRRogers LakeFlathead	NR	13.6 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRDickey LakeFlathead	NR	17.7 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRMcgilvray LakeFlathead	NR	21 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRFish LakeFlathead	NR	16.6 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRLower Stillwater LakeFlathead	NR	21 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRSkyles LakeFlathead	NR	17 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRBeaver LakeFlathead	NR	18.8 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRUpper Whitefish LakeFlathead	NR	20.5 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRBootjack LakeFlathead	NR	20.8 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRFoy LakeFlathead	NR	17.5 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake BlaineFlathead	NR	17.1 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRAshley LakeFlathead	NR	33.1 ft	No recent samples	No recent samples	No recent samples	✓ Public
	NRHanson-Doyle LakeFlathead	NR	21.8 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRAbbot LakeFlathead	NR	15 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRPeterson LakeFlathead	NR	14.9 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake FiveFlathead	NR	16 ft	No recent samples	No recent samples	No recent samples	✓ Public
	NRMurray LakeFlathead	NR	22 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRDollar LakeFlathead	NR	19.2 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRUpper Stillwater LakeFlathead	NR	21.9 ft	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake of the WoodsFlathead	NR	No recent samples	5 µg/L	0.1 µg/L	No recent samples	Not recorded
	NRLake McdonaldFlathead	NR	No recent samples	No recent samples	0.7 µg/L	No recent samples	Not recorded
	NRLost Loon LakeFlathead	NR	No recent samples	10.1 µg/L	2.6 µg/L	No recent samples	Not recorded
	NRHubbart ReservoirFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLittle McGregor LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMcGregor LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLynch LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDahl LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRPearson ReservoirFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSmith LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	✓ Public
	NRLake MonroeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLone LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMiddle Foy LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMcWenneger SloughFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NREgan SloughFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRChurch SloughFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWileys SloughFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFennon SloughFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake of the WoodsFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMud LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMargaret LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHandkerchief LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRPilgrim LakesFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBirch LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBlack LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWildcat LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRClayton LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHungry Horse ReservoirFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLion LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLore LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBowser LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBoyle LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSpoon LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHarrison LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLincoln LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake Ellen WilsonFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRAvalanche LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLogging LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRTrout LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRArrow LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake EvangelineFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRRuger LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCerulean LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRGyrfalcon LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRGrace LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLower Quartz LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMiddle Quartz LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRQuartz LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBowman LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRWinona LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRCyclone LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFinger LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDuck LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRDog LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRTepee LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLong Bow LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRUpper Kintla LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRPocket LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRHidden LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBuffalo Woman LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBeaver Woman LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRStriped Elk LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRLake IsabelFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRStanton LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMarion LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMoose LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRElk LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBradley LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRFlotilla LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRScott LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRSunburst LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRPalisade LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRMud LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded
	NRBig Salmon LakeFlathead	NR	No recent samples	No recent samples	No recent samples	No recent samples	Not recorded

NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.

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Other Counties in Montana

Missoula County

46 lakes · Avg grade B

Carbon County

38 lakes · Avg grade B

Yellowstone County

6 lakes · Avg grade B

Big Horn County

4 lakes · Avg grade C

Lake County

38 lakes · Avg grade C

Broadwater County

2 lakes · Avg grade C

See how Flathead County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..

Source: EPA National Aquatic Resource Surveys, 2026.