Impaired Lakes in Washington
36 of 49 graded Washington lakes (73%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 3 have an approved TMDL restoration plan.
Top Causes of Impairment in Washington
Reading the Washington impairment landscape
73% of Washington's tracked lakes — 36 of 49 — appear on the EPA Clean Water Act §303(d) impaired-waters list. At that share, impairment is the default state rather than an exception: the majority of lakes are flagged for at least one pollutant exceeding water-quality standards. Trip-planning for clean water in Washington typically requires checking impairment status as a first filter, not as an edge case.
The leading impairment category in Washington is Nutrients (phosphorus, nitrogen) — nutrient enrichment, typically from agricultural fertilizer runoff, septic discharge, or stormwater carrying lawn-care residue. Nutrient-impaired lakes can still be safe for contact recreation in many conditions, but they're prone to algal blooms (including potentially toxic cyanobacteria) during warm-water periods. Check the state's beach-monitoring or harmful-algal-bloom dashboard before swimming on nutrient-impaired waters in summer.
Impaired-waters listings come from the state environmental agency's §303(d) submission to EPA, refreshed on a roughly 2-year cycle. A listed lake stays on the list until either a TMDL is established and the cleanup completes, or subsequent monitoring shows the pollutant concentrations no longer exceed water-quality standards. The list below reflects the most recent available Washington submission to the EPA Assessment, Total Maximum Daily Load Tracking and Implementation System (ATTAINS) dataset.
All 36 EPA-Listed Impaired Lakes in Washington
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Moses Lake | Grant | B | Temperature | — |
| Weallup Lake | Snohomish | C | Nuisance exotic species | — |
| Lake: Deep Lake | Thurston | C | Nuisance exotic species | — |
| Lake: Lake St. Clair @ East Basin | Thurston | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Lake: Ward Lake | Thurston | D | Mercury, PCBs | — |
| Lake: Lawrence Lake @ Big Basin | Thurston | D | Nutrients (phosphorus, nitrogen) | — |
| Lake: Black Lake @ South Basin | Thurston | D | Nutrients (phosphorus, nitrogen) | — |
| Lake: Hicks Lake | Thurston | D | Nuisance exotic species | — |
| Lake: Long Lake @ Lo | Thurston | D | Dioxins, Mercury, Nuisance exotic species +1 more | — |
| Lake: Lake St. Clair @ Sw Basin | Thurston | D | Mercury, Nutrients (phosphorus, nitrogen) | — |
| Lake: Pattison Lake | Thurston | D | Nutrients (phosphorus, nitrogen) | — |
| Lake: Offutt Lake | Thurston | D | Mercury | — |
| Lake | Thurston | F | Nuisance exotic species, Nutrients (phosphorus, nitrogen) | — |
| Vancouver Lake | Clark | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake Sammamish | King | NR | Mercury, PCBs | — |
| Gravelly Lake | Pierce | NR | Nutrients (phosphorus, nitrogen) | — |
| Lacamas Lake | Clark | NR | Nuisance exotic species, Nutrients (phosphorus, nitrogen) | — |
| American Lake | Pierce | NR | Dioxins, Nuisance exotic species, Pathogens (E. coli, fecal) +2 more | — |
| Steilacoom Lake | Pierce | NR | Nutrients (phosphorus, nitrogen) | — |
| Carp Lake | Pierce | NR | Nutrients (phosphorus, nitrogen) | — |
| Waughop Lake | Pierce | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake Beecher | Snohomish | NR | Nutrients (phosphorus, nitrogen) | — |
| Lake Roesiger | Snohomish | NR | Nuisance exotic species | — |
| Debra Jane Lake | Pierce | NR | Nuisance exotic species | — |
| Liberty Lake | Spokane | NR | Mercury, Nuisance exotic species, Nutrients (phosphorus, nitrogen) +2 more | ✓ |
| Angle Lake | King | NR | Pathogens (E. coli, fecal) | — |
| Lake Louise | Pierce | NR | Nutrients (phosphorus, nitrogen) | — |
| Bonney Lake | Pierce | NR | Nuisance exotic species | — |
| Billy Clapp Lake | Grant | NR | Nuisance exotic species | — |
| Spokane Arm -Potential Discharge Location Lake | Stevens | NR | Total toxics | — |
| Lake: Capitol Lake @ Mid-Middle Basin | Thurston | NR | Oxygen depletion (low DO), Pathogens (E. coli, fecal) | ✓ |
| Jsl Lake | Snohomish | NR | Nuisance exotic species, Nutrients (phosphorus, nitrogen) | — |
| Lake: Capitol Lake @ Mid-North Basin | Thurston | NR | Oxygen depletion (low DO), Pathogens (E. coli, fecal) | ✓ |
| Lake: Barnes Lake | Thurston | NR | Nutrients (phosphorus, nitrogen) | — |
| Scooteney Reservoir Boat Ramp | Franklin | NR | Nuisance exotic species, Pesticides | — |
| Settling Pond | Clallam | NR | Pathogens (E. coli, fecal) | — |
Frequently Asked Questions
How many lakes are impaired in Washington?
36 of 49 graded Washington lakes (73%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 29 are on the federal Clean Water Act §303(d) list and 3 have an approved Total Maximum Daily Load (TMDL) restoration plan.
What does Clean Water Act §303(d) mean?
Section 303(d) of the federal Clean Water Act requires every state to identify waters that don't meet water quality standards even after pollution control measures. Each listed water must then have a Total Maximum Daily Load (TMDL) developed — a plan that caps how much of each pollutant can enter the waterbody. The "303(d) list" is the impaired-waters list. The EPA reviews each state's list every two years.
What are the top causes of impairment in Washington?
The most common causes flagged across Washington's impaired lakes are: Nutrients (phosphorus, nitrogen) (18 lakes); Nuisance exotic species (14 lakes); Mercury (7 lakes); Pathogens (E. coli, fecal) (5 lakes); PCBs (4 lakes); Pesticides (3 lakes). Mercury is widespread in fish tissue across the upper Midwest from atmospheric deposition. Nutrient impairment (phosphorus, nitrogen) typically reflects agricultural runoff and urban stormwater.
Can I swim in an impaired lake?
It depends on the cause of impairment. A lake impaired for "mercury in fish tissue" is generally safe to swim in — the warning is about long-term consumption of fish. A lake impaired for "pathogens" (E. coli) or "algal growth" may pose a swimming risk and often has a separate beach advisory. Check the cause categories listed for each lake below, and consult your state health department's beach monitoring program for current advisories.
Where does this impairment data come from?
Every impairment record on this page comes from the EPA's ATTAINS (Assessment and TMDL Tracking and Implementation System) public dataset, the federal repository of state-reported water quality assessments. EPA ATTAINS is published as GeoParquet files on the EPA Office of Water S3 bucket and refreshed several times per year. Causes and use-support codes follow EPA's standard taxonomy.
More on impaired waters
What it means when a lake is listed as impaired, why mercury is the most common reason, and why a listed lake can still be clear water with a good grade.
Why states issue fish-consumption advisories, which contaminants — mercury, PCBs, PFAS — drive them, and how to eat the fish you catch more safely.
How phosphorus and nutrient runoff drive algae growth and turn lakes green, where the nutrients come from, and what it means for a lake's grade.
Which lakes are actually improving: multi-year EPA monitoring trends, the named recoveries still in progress, and what it takes to move a letter grade.
Data source
Impairment data from the EPA ATTAINS (Assessment and TMDL Tracking and Implementation System) public dataset. Assessment unit IDs are matched to LakeQuality lakes by name and proximity; some lakes may not appear here if their ATTAINS name doesn't match our naming convention. For an official query, consult .