The State of Colorado's Lakes 2026

Cleanest lakes in Colorado

Highest combined water-quality score, 2026.

1. 1.APueblo Reservoir — Pueblo County6.5 ft clarity · 15 µg/L P · 5 µg/L chl-a
2. 2.CWillow Creek Reservoir — Grand County3.9 ft clarity · 76 µg/L P · 2 µg/L chl-a
3. 3.CWolford Mountain Reservoir — Grand County7.5 ft clarity · 13 µg/L P · 2 µg/L chl-a
4. 4.CGrand Lake — Grand County8.7 ft clarity · 14 µg/L P · 3 µg/L chl-a
5. 5.DShadow Mountain Lake — Grand County7.9 ft clarity · 20 µg/L P · 5 µg/L chl-a
6. 6.DBlue Mesa Reservoir — Gunnison County11.5 ft clarity · 35 µg/L P · 4 µg/L chl-a
7. 7.DDillon Reservoir — Summit County11.6 ft clarity · 46 µg/L P · 3 µg/L chl-a
8. 8.DDeweese Reservoir — Custer County5.2 ft clarity · 42 µg/L P · 14 µg/L chl-a
9. 9.DWindy Gap Reservoir — Grand County52 µg/L P · 3 µg/L chl-a
10. 10.DHorse Creek Outlet Lake — Weld County460 µg/L P · 28 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

1. 1.FProspect Lake — Weld County300 µg/L P · 43 µg/L chl-a
2. 2.DShadow Mountain Lake — Grand County7.9 ft clarity · 20 µg/L P · 5 µg/L chl-a
3. 3.DBlue Mesa Reservoir — Gunnison County11.5 ft clarity · 35 µg/L P · 4 µg/L chl-a
4. 4.DDillon Reservoir — Summit County11.6 ft clarity · 46 µg/L P · 3 µg/L chl-a
5. 5.DDeweese Reservoir — Custer County5.2 ft clarity · 42 µg/L P · 14 µg/L chl-a
6. 6.DWindy Gap Reservoir — Grand County52 µg/L P · 3 µg/L chl-a
7. 7.DHorse Creek Outlet Lake — Weld County460 µg/L P · 28 µg/L chl-a
8. 8.DStagecoach Lake — Routt County50 µg/L P
9. 9.CWillow Creek Reservoir — Grand County3.9 ft clarity · 76 µg/L P · 2 µg/L chl-a
10. 10.CWolford Mountain Reservoir — Grand County7.5 ft clarity · 13 µg/L P · 2 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

1. 1.FNorth Sterling Reservoir — Logan County198 µg/L chlorophyll-a
2. 2.NRTurks Pond — Baca County140 µg/L chlorophyll-a
3. 3.FProspect Lake — El Paso County81 µg/L chlorophyll-a
4. 4.FProspect Lake — Weld County43 µg/L chlorophyll-a
5. 5.NREquestrian Park Pond — Douglas County36 µg/L chlorophyll-a
6. 6.NRBerkeley Lake — Denver County34 µg/L chlorophyll-a
7. 7.NRPrewitt Reservoir — Washington County32 µg/L chlorophyll-a
8. 8.DHorse Creek Outlet Lake — Weld County28 µg/L chlorophyll-a
9. 9.DWindsor Lake — Weld County25 µg/L chlorophyll-a
10. 10.DJackson Reservoir — Morgan County22 µg/L chlorophyll-a

Trending lakes

Improving

1. 1.APueblo Reservoir — Pueblo County
2. 2.BLake Granby Dam Bottom — Grand County
3. 3.CWillow Creek Reservoir — Grand County
4. 4.CGrand Lake — Grand County
5. 5.CLake Nighthorse — La Plata County
6. 6.DBlue Mesa Reservoir — Gunnison County
7. 7.DBig Meadows Reservoir — Mineral County
8. 8.DVega Reservoir — Mesa County

Declining

1. 1.FProspect Lake — Weld County
2. 2.DJackson Reservoir — Morgan County
3. 3.DBeaver Creek Reservoir — Rio Grande County
4. 4.DHorse Creek Outlet Lake — Weld County
5. 5.DStagecoach Lake — Routt County
6. 6.CWolford Mountain Reservoir — Grand County
7. 7.ACrystal Reservoir — Montrose County
8. 8.NRCatamount Lake Top — Routt County