San Juan County Lake Quality
Colorado, 2 lakes, average grade A (Excellent)
San Juan County has 2 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. The county's average grade is A — among the cleanest in {{stateName}}. 2 lakes pull an A on their own, and almost none fall into the D or F brackets.
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. Little Eldorado Lake (A) is the cleanest in the county.
Quick Answers for San Juan County
Planning a trip? Check special fishing regulations for Little Eldorado Lake — or check the official Colorado fishing regulations.
All Lakes in San Juan County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Little Eldorado Lake | A | - | 4 µg/L |
| 2 | White Dome Lake | A | - | 5 µg/L |
Other Counties in Colorado
See how San Juan 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 San Juan County
Top-rated places to stay near San Juan County
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip to San Juan County?
Get lake water-quality report cards plus the best cabin & lodging deals near San Juan County — straight to your inbox. No spam, unsubscribe anytime.
Source: EPA National Aquatic Resource Surveys, 2026.