Costilla County Lake Quality
Colorado, 6 lakes — no lake here has enough monitoring data for a grade
Costilla County has 6 monitored 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. No lake in Costilla County has enough sampling behind it for an A–F grade yet. The 6 monitored lakes below carry whatever clarity, phosphorus, and chlorophyll-a measurements exist.
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.
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Quick Answers for Costilla County
Planning a trip? Check special fishing regulations for Mountain Home Reservoir — or check the official Colorado fishing regulations.
All Lakes in Costilla County
6 lakes · 0 graded, 6 not rated0 graded lakes · 6 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| NRMountain Home ReservoirCostilla | NR | 14.4 ft | 17 µg/L | 6.2 µg/L | No recent samples | ✓ Public | |
| NRSmith ReservoirCostilla | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRForbes Park LakeCostilla | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRWillow Creek ReservoirCostilla | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRStabilization ReservoirCostilla | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRSanchez ReservoirCostilla | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded |
NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
Lake Match
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Other Counties in Colorado
See how Costilla County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario and Québec), and 38 other country hubs..
Source: EPA National Aquatic Resource Surveys, 2026.