Updated Aug 2026
Washington Lake Water Quality
Water quality grades for 18 of the 792 lakes we list here, across 35 counties.
Grade Distribution
All 792 Washington lakes in the index: 18 (2.3%) carry an A–F grade and 774 (97.7%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
Lake Map
Get Washington water-quality updates
New grades, clarity readings, and algae advisories for Washington lakes as samples come in. Unsubscribe anytime.
Where to stay near Washington's top-graded lakes
Cabins, resorts, and vacation rentals around Fdr Lake and the other top-graded Washington lakes pinned on the map. Live availability and prices.
Top-rated places to stay near Fdr Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Explore Washington Lakes
Washington reports, fishing & travel
Reservoirs in Washington
View all 9 reservoirs →9 of 792 Washington lakes (1%) are man-made reservoirs in the USACE National Inventory of Dams. 6 carry a High or Significant hazard rating. The oldest matched dam dates to 1911.
EPA-Impaired Lakes in Washington
View all 35 impaired lakes →35 of 792 Washington lakes (4%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 3 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Washington Fishing & Recreation
Licenses, regulations, records, and where to fish across Washington.
Counties
All 35 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.
Washington Lakes Needing Attention
18 lakes18 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | FLake | Thurston | F | No recent samples |
| 2 | DLake | Thurston | D | No recent samples |
| 3 | DLake | Thurston | D | No recent samples |
| 4 | DLake | Thurston | D | No recent samples |
| 5 | DLake | Thurston | D | No recent samples |
| 6 | DLake | Thurston | D | No recent samples |
| 7 | DLake | Thurston | D | No recent samples |
| 8 | DLake | Thurston | D | No recent samples |
| 9 | DLake | Thurston | D | No recent samples |
| 10 | DLake | Thurston | D | No recent samples |
| 11 | CRimrock Reservoir | Yakima | C | No recent samples |
| 12 | CLake | Thurston | C | No recent samples |
| 13 | CWeallup Lake | Snohomish | C | No recent samples |
| 14 | CLake | Thurston | C | No recent samples |
| 15 | BMoses Lake | Grant | B | No recent samples |
| 16 | BRoss Lake | Whatcom | B | No recent samples |
| 17 | ABanks Lake | Grant | A | 19.4 ft |
| 18 | AFdr Lake | Lincoln | A | 16.2 ft |
18 of the 792 Washington lakes in this index carry an A–F water-quality grade, spread over 35 counties. Those grades rest on measurements from the Washington State Department of Ecology, alongside federal programs and volunteer monitoring networks. The rest are listed for their size, depth and location, without enough recent nutrient or algae sampling behind them to support a letter.
By surface area the largest lake here is Banks Lake, at about 27,000 acres, and 75 of the lakes in this index cover more than 500 acres. Size is worth knowing before you go: a large deep basin buffers nutrient inputs by sheer volume, while a shallow one warms quickly and can turn over its whole water column in a single summer storm. Lincoln ranks highest on average county grade (A), and Thurston sits lowest. With only 35 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.
More on lake water quality
A data snapshot of the lakes we grade: how the A–F distribution breaks down, the clearest and the greenest states, and where the water is improving.
How lakes are graded A–F on nutrients and algae using EPA ecoregion condition classes, what each letter means in the water, and why an A is not a clearance.
The cleanest and dirtiest U.S. lakes in the monitoring record, ranked on EPA nutrient and algae condition classes across thousands of graded lakes.
The clearest lakes in America, ranked by measured Secchi depth in feet from EPA monitoring data — and why the famously clear lakes are missing.