San Juan County Lake Quality
Washington, 9 lakes — no lake here has enough monitoring data for a grade
San Juan County holds 9 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. No lake in San Juan County has enough sampling behind it for an A–F grade yet. The 9 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 San Juan County
Planning a trip? Check special fishing regulations for Spencer Lake — or check the official Washington fishing regulations.
All Lakes in San Juan County
9 lakes · 0 graded, 9 not rated0 graded lakes · 9 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| NRSpencer LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRHummel LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRZyistra LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRTrout LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRRoche Harbor LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRMartin LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRHorseshoe LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRMountain LakeSan Juan | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRCascade LakeSan Juan | 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.
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Other Counties in Washington
See how San Juan 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, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..
Source: EPA National Aquatic Resource Surveys, 2026.