King County Lake Quality
Washington, 6 lakes, average grade B (Good)
King County has 6 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. With an average grade of B, King County sits comfortably above the {{stateName}} median.
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. Nla Lake (A) is the cleanest in the county.
Quick Answers for King County
Planning a trip? Check special fishing regulations for Nla Lake — or check the official Washington fishing regulations.
All Lakes in King County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Nla Lake | A | 77.4 ft | 1.9 µg/L |
| 2 | Angle Lake | A | 20 ft | - |
| 3 | Lake Sammamish | B | 11.5 ft | - |
| 4 | Nla Lake | C | 12 ft | 14011.8 µg/L |
| 5 | Nla Lake | C | 7.7 ft | 6024.7 µg/L |
| 6 | Nla Lake | C | 1.6 ft | 29.7 µg/L |
Other Counties in Washington
See how King County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 34 states.
Where to stay near King County
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Source: EPA National Aquatic Resource Surveys, 2026.