Summit County Lake Quality
Colorado, 3 lakes, average grade B (Good)
Only 3 lakes in Summit County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. With an average grade of B, Summit County sits comfortably above the {{stateName}} median.
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 Dillon Reservoir (B); the most-stressed is Dillon Reservoir (B).
Quick Answers for Summit County
Planning a trip? Check special fishing regulations for Dillon Reservoir — or check the official Colorado fishing regulations.
All Lakes in Summit County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Dillon Reservoir | B | 11.6 ft | - |
| 2 | Green Mountain Reservoir | B | 11.5 ft | - |
Other Counties in Colorado
See how Summit County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 12 states.
Where to stay near Summit County
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Source: EPA National Aquatic Resource Surveys, 2026.