Updated Jul 2026
Washington Lake Water Quality
Water quality grades for 89 monitored lakes across 27 counties.
{{stateName}} has 89 graded lakes in our dataset, sampled across 27 counties, drawing on monitoring by {{agency}} plus federal and volunteer measurements. Roughly 31% of the state's graded lakes carry an A — 28 lakes that earn the top bracket on the combined Secchi/phosphorus/chlorophyll-a rubric. That share is high by national standards and reflects the depth and natural clarity of glacial lakes in the region.
A meaningful share of the state's monitored lakes register as hypereutrophic — heavily nutrient-loaded, frequent blooms, low summer transparency. These are usually shallow, surrounded by row-crop agriculture, with little volume to buffer the inputs. Lincoln ranks highest on average county grade (A). Clark sits lowest. With only 27 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
How Washington’s 89 graded lakes break down from A (excellent) to F.
Top-Graded Washington Lakes
The highest water-quality grades in Washington — clarity, depth, and A-F grade at a glance.
Ross Lake
Whatcom County, Washington
See grade for Ross Lake →Nla Lake
Skamania County, Washington
See grade for Nla Lake →Nla Lake
King County, Washington
See grade for Nla Lake →Nla Lake
Chelan County, Washington
See grade for Nla Lake →Nla Lake
Snohomish County, Washington
See grade for Nla Lake →Nla Lake
Pierce County, Washington
See grade for Nla Lake →Fdr Lake
Lincoln County, Washington
See grade for Fdr Lake →Fdr Lake
Okanogan County, Washington
See grade for Fdr Lake →Gravelly Lake
Pierce County, Washington
See grade for Gravelly Lake →Lake Map
Explore Washington Lakes
Washington reports, fishing & travel
Washington Fishing & Recreation
Licenses, regulations, records, and where to fish across Washington.
Counties
All 27 Washington counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Top 25 Cleanest Lakes
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Ross Lake | Whatcom | A | 18.8 ft |
| 2 | Nla Lake | Skamania | A | 26.3 ft |
| 3 | Nla Lake | King | A | 77.4 ft |
| 4 | Nla Lake | Chelan | A | 42.8 ft |
| 5 | Nla Lake | Snohomish | A | 22.6 ft |
| 6 | Nla Lake | Pierce | A | - |
| 7 | Fdr Lake | Lincoln | A | 16.2 ft |
| 8 | Fdr Lake | Okanogan | A | 21.5 ft |
| 9 | Gravelly Lake | Pierce | A | 25.4 ft |
| 10 | Banks Lake | Grant | A | 19.4 ft |
| 11 | American Lake | Pierce | A | 19.7 ft |
| 12 | Steilacoom Lake | Pierce | A | 17.4 ft |
| 13 | Lake Roesiger | Snohomish | A | 17.1 ft |
| 14 | Angle Lake | King | A | 20 ft |
| 15 | Fdr Lake | Grant | A | 28.2 ft |
| 16 | Lake Louise | Pierce | A | 17.1 ft |
| 17 | Billy Clapp Lake | Grant | A | 16.4 ft |
| 18 | Lake: Ward Lake | Thurston | A | - |
| 19 | Lake: Summit Lake | Thurston | A | - |
| 20 | Lake: Deep Lake | Thurston | A | - |
| 21 | Nla Upper Lake | Grays Harbor | A | - |
| 22 | Rimrock Reservoir | Yakima | A | - |
| 23 | Nla Lake | Grant | A | 12.8 ft |
| 24 | Fdr Lake | Ferry | A | 13.5 ft |
| 25 | Fdr Lake | Ferry | A | 19 ft |
25 Lakes Needing Attention
| Rank | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | Lake | Thurston | F | - |
| 2 | Nla Lake | Grant | F | 1.1 ft |
| 3 | Nla Lake | Clark | F | 3.3 ft |
| 4 | Nla Lake | Lewis | F | 6.3 ft |
| 5 | Nla Lake | Grant | D | 2.2 ft |
| 6 | Nla Lake | Thurston | D | 4.9 ft |
| 7 | Vancouver Lake | Clark | D | 1.2 ft |
| 8 | Jsl Lake | Snohomish | D | - |
| 9 | Brook Lake | Grant | D | - |
| 10 | Bonney Lake | Pierce | D | 5.2 ft |
| 11 | Debra Jane Lake | Pierce | D | 3.9 ft |
| 12 | Lake Beecher | Snohomish | D | 5.6 ft |
| 13 | Waughop Lake | Pierce | D | 5.6 ft |
| 14 | Carp Lake | Pierce | D | 6.6 ft |
| 15 | Lacamas Lake | Clark | D | 4.4 ft |
| 16 | Nla Lake | Kittitas | D | 3.1 ft |
| 17 | Nla Lake | Stevens | D | 7.7 ft |
| 18 | Nla Lake | Pacific | D | 3.3 ft |
| 19 | Nla Lake | Spokane | D | 7.2 ft |
| 20 | Nla Lake | Thurston | D | 7.7 ft |
| 21 | Nla Lake | San Juan | D | 6.1 ft |
| 22 | Nla Lake | King | C | 1.6 ft |
| 23 | Weallup Lake | Snohomish | C | - |
| 24 | Nla Lake | Ferry | C | - |
| 25 | Nla Lake | Mason | C | - |
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Source: EPA National Aquatic Resource Surveys, 2026.