Updated Jul 2026
Colorado Lake Water Quality
Water quality grades for 89 monitored lakes across 44 counties.
{{stateName}} has 89 graded lakes in our dataset, sampled across 44 counties, drawing on monitoring by {{agency}} plus federal and volunteer measurements. About 17% of graded {{stateName}} lakes earn an A. The bulk sit in the middle B–C range; 51% 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. Montrose ranks highest on average county grade (A). Weld sits lowest. With only 44 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
How Colorado’s 89 graded lakes break down from A (excellent) to F.
Top-Graded Colorado Lakes
The highest water-quality grades in Colorado — clarity, depth, and A-F grade at a glance.
Standley Lake
Jefferson County, Colorado
See grade for Standley Lake →Lake Nighthorse
La Plata County, Colorado
See grade for Lake Nighthorse →Crystal Reservoir
Montrose County, Colorado
See grade for Crystal Reservoir →Island Lake
Delta County, Colorado
See grade for Island Lake →Rampart Reservoir
El Paso County, Colorado
See grade for Rampart Reservoir →Turquoise Reservoir
Lake County, Colorado
See grade for Turquoise Reservoir →Little Eldorado Lake
San Juan County, Colorado
See grade for Little Eldorado Lake →Upper Sunlight Lake
La Plata County, Colorado
See grade for Upper Sunlight Lake →Ned Wilson Lake
Rio Blanco County, Colorado
See grade for Ned Wilson Lake →Lake Map
Explore Colorado Lakes
Colorado reports, fishing & travel
Colorado Fishing & Recreation
Licenses, regulations, records, and where to fish across Colorado.
Counties
All 44 Colorado counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Standley Lake | Jefferson | A | 20.5 ft |
| 2 | Lake Nighthorse | La Plata | A | 18.7 ft |
| 3 | Crystal Reservoir | Montrose | A | 15.4 ft |
| 4 | Island Lake | Delta | A | 16.7 ft |
| 5 | Rampart Reservoir | El Paso | A | 28.5 ft |
| 6 | Turquoise Reservoir | Lake | A | 16.1 ft |
| 7 | Little Eldorado Lake | San Juan | A | - |
| 8 | Upper Sunlight Lake | La Plata | A | - |
| 9 | Ned Wilson Lake | Rio Blanco | A | - |
| 10 | Upper Grizzly Lake | La Plata | A | - |
| 11 | Seven Lakes | Jackson | A | - |
| 12 | White Dome Lake | San Juan | A | - |
| 13 | Arkansas Lake | Prowers | A | - |
| 14 | N St Vrain Lake | Boulder | A | - |
| 15 | Lake Granby | Grand | A | 12.7 ft |
| 16 | Pueblo Reservoir | Pueblo | B | 6.7 ft |
| 17 | Wolford Mountain Reservoir | Grand | B | 8.3 ft |
| 18 | Grand Lake | Grand | B | 8.9 ft |
| 19 | Summit Lake | Jackson | B | 12.1 ft |
| 20 | Blue Mesa Reservoir | Gunnison | B | 11.5 ft |
| 21 | Skaguay Reservoir | Teller | B | 12.5 ft |
| 22 | Dillon Reservoir | Summit | B | 11.6 ft |
| 23 | Pearl Lake | Routt | B | 14.1 ft |
| 24 | Mountain Home Reservoir | Costilla | B | 14.4 ft |
| 25 | Antero Reservoir | Park | B | 14.8 ft |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Arkansas Lake | Prowers | F | - |
| 2 | Arkansas Lake | El Paso | F | - |
| 3 | Milton Reservoir | Weld | F | 2.6 ft |
| 4 | Lake Henry | Crowley | F | 1.3 ft |
| 5 | Adobe Creek Reservoir | Kiowa | F | 1.7 ft |
| 6 | Miramonte Reservoir | San Miguel | F | 2.8 ft |
| 7 | Lake Meredith | Crowley | F | 1.6 ft |
| 8 | John Martin Reservoir | Bent | F | 3.1 ft |
| 9 | Equestrian Park Pond | Douglas | F | 3 ft |
| 10 | Turks Pond | Baca | F | 0.7 ft |
| 11 | Nee Noshe Reservoir | Kiowa | F | 1.2 ft |
| 12 | Berkeley Lake | Denver | F | 1 ft |
| 13 | Highline Lake | Mesa | F | 3 ft |
| 14 | Prewitt Reservoir | Washington | F | 1.8 ft |
| 15 | Jumbo Reservoir | Logan | F | 2.1 ft |
| 16 | Union Reservoir | Weld | F | 3.2 ft |
| 17 | Jackson Reservoir | Morgan | F | 2.1 ft |
| 18 | North Sterling Reservoir | Logan | F | 1.1 ft |
| 19 | Prospect Lake | Weld | F | - |
| 20 | Prospect Lake | El Paso | F | 1.6 ft |
| 21 | Windsor Lake | Weld | F | 2 ft |
| 22 | Elkhead Reservoir | Moffat | D | 5.2 ft |
| 23 | Steamboat Lake | Routt | D | 6.6 ft |
| 24 | Martin Lake | Huerfano | D | 4.8 ft |
| 25 | Road Canyon Reservoir | Hinsdale | D | 5.6 ft |
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Source: EPA National Aquatic Resource Surveys, 2026.