Updated Jul 2026

Wyoming Lake Water Quality

Water quality grades for 243 monitored lakes across 19 counties.

243 {{stateName}} lakes carry a grade. Most of the input data flows through monitoring run by {{agency}}, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. About 17% of graded {{stateName}} lakes earn an A. The bulk sit in the middle B–C range; 27% fall into D or F, almost all of those in counties where row-crop agriculture dominates the watershed.

The state's lakes lean eutrophic: enough nutrient input to support an active algal community, with the trade-offs in clarity and dissolved oxygen that come with it. Weston ranks highest on average county grade (A). Campbell sits lowest. With only 19 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.

Rank	Lake	County	Grade	Clarity
1	Flaming Gorge Reservoir	Sweetwater	A	22 ft
2	Nla Lake	Sublette	A	25.3 ft
3	West Thumb Lake	Teton	A	31.2 ft
4	Yellowstone Lake	Teton	A	28.7 ft
5	Yellowstone Lake	Teton	A	26.2 ft
6	Flaming Gorge-Green River Lake	Sweetwater	A	18.4 ft
7	Yellowstone Lake @ East Side of Stevenson Island	Teton	A	27.1 ft
8	Flaming Gorge Lake	Sweetwater	A	17.4 ft
9	Yellowstone Lake	Teton	A	25.4 ft
10	Yellowstone Lake	Teton	A	25.4 ft
11	Fontenelle Reservoir	Lincoln	A	15 ft
12	Lake Desmet Lpd	Johnson	A	39.1 ft
13	Lake Desmet Rtpd	Johnson	A	34.6 ft
14	Half Moon Lake	Sublette	A	22.2 ft
15	Lower New Fork Lake	Sublette	A	22 ft
16	Boulder Lake	Sublette	A	27.7 ft
17	Fremont Lake	Sublette	A	42.8 ft
18	Lak Reservoir	Weston	A	22.4 ft
19	Worthen Meadows Reservoir	Fremont	A	15.9 ft
20	Inlet Arizona Island Lake	Teton	A	17.5 ft
21	Leeks Marina North Lake	Teton	A	16.4 ft
22	Moran Bay Lake	Teton	A	18.3 ft
23	West Newton Lake	Park	A	17.7 ft
24	Hog Park Reservoir	Carbon	A	17.9 ft
25	Atlantic Rim Reservoir	Carbon	A	-

Rank	Lake	County	Grade	Clarity
1	Burlington Lake D	Campbell	F	-
2	Unnamed Reservoir	Big Horn	F	-
3	Yellowtail Reservoir Rpd	Big Horn	F	-
4	Kinnear Lake D	Fremont	F	-
5	Buffalo Bill Reservoir	Park	F	-
6	Beck Lake D	Park	F	-
7	Spring Lake D	Carbon	F	-
8	Scotty Lake	Sweetwater	F	-
9	Wheatland Reservoir Rtpd	Albany	F	-
10	Brooks Lake	Fremont	F	-
11	Brooks Lake Creek	Fremont	F	-
12	Brooks Lake	Fremont	F	-
13	Bump-Sullivan Reservoir	Goshen	F	0.2 ft
14	Goshen Hole Reservoir	Goshen	F	1.1 ft
15	Green River Inflow Lake	Sweetwater	F	1.6 ft
16	Horseshoe Reservoir	Big Horn	F	1.8 ft
17	Festo Lake	Platte	F	0.8 ft
18	Woodruff Narrows Reservoir	Uinta	F	0.9 ft
19	Glendo Reservoir Riverine Littoral	Platte	F	1.1 ft
20	Fontenelle Reservoir Green River Inflow	Lincoln	F	3.1 ft
21	Nla Lake	Teton	F	4.9 ft
22	Brooks Lake	Fremont	D	6 ft
23	Hereford Reservoir	Laramie	D	3.6 ft
24	Buffalo Bill Reservoir Transitional Pelagic	Park	D	2.8 ft
25	Big Sandy Reservoir Rtpd	Sublette	D	0.7 ft

Wyoming Lake Water Quality

Grade Distribution

Top-Graded Wyoming Lakes

Flaming Gorge Reservoir

Nla Lake

West Thumb Lake

Yellowstone Lake

Yellowstone Lake

Flaming Gorge-Green River Lake

Yellowstone Lake @ East Side of Stevenson Island

Flaming Gorge Lake

Yellowstone Lake

Lake Map

Explore Wyoming Lakes

Wyoming reports, fishing & travel

Wyoming Fishing & Recreation

Counties

Top 25 Cleanest Lakes

25 Lakes Needing Attention

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