Impaired Lakes in Oregon
49 of 73 graded Oregon lakes (67%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 22 have an approved TMDL restoration plan.
Top Causes of Impairment in Oregon
Reading the Oregon impairment landscape
67% of Oregon's tracked lakes — 49 of 73 — 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 Oregon typically requires checking impairment status as a first filter, not as an edge case.
The leading impairment cause in Oregon is Algal growth. Each impairment category carries its own use-restriction implications — some affect fish consumption, some affect swimming, some affect aquatic-life habitat. Click through to the specific lake records below for the pollutant list and the TMDL (Total Maximum Daily Load) status, which determines whether a cleanup plan is in place.
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 Oregon submission to the EPA Assessment, Total Maximum Daily Load Tracking and Implementation System (ATTAINS) dataset.
All 49 EPA-Listed Impaired Lakes in Oregon
| Lake | County | Grade | Causes | TMDL |
|---|---|---|---|---|
| Crescent Lake | Klamath | A | Oxygen depletion (low DO) | — |
| Applegate Lake | Jackson | A | Mercury, Temperature | ✓ |
| Galesville Reservoir | Douglas | A | Mercury | — |
| Wallowa Lake | Wallowa | A | Pathogens (E. coli, fecal), Temperature | ✓ |
| Henry Hagg Lake | Washington | A | Oxygen depletion (low DO) | ✓ |
| Green Peter Lake | Linn | A | Temperature | ✓ |
| Detroit Lake | Marion | B | Algal growth | ✓ |
| Blue River Lake | Lane | B | Algal growth | ✓ |
| Odell Lake | Klamath | C | Algal growth, Mercury, Oxygen depletion (low DO) +1 more | — |
| Billy Chinook Reservoir | Jefferson | C | Algal growth, Hydrologic alteration, pH / acidity | — |
| Wickiup Reservoir | Deschutes | C | Algal growth, Temperature | — |
| Lost Creek Lake | Jackson | C | Algal growth | ✓ |
| Willow Lake | Jackson | C | Algal growth | — |
| Emigrant Lake | Jackson | C | Mercury, Temperature | ✓ |
| Foster Lake | Linn | C | Temperature | ✓ |
| East Lake Hot Springs Boat Ramp | Deschutes | C | Mercury | — |
| Bully Creek Lake | Malheur | D | Mercury, Metals (other than mercury), Toxic inorganics | — |
| Deschutes River Arm Lake | Jefferson | D | Algal growth, Hydrologic alteration, pH / acidity | — |
| Crane Prairie Reservoir | Deschutes | D | Algal growth, Oxygen depletion (low DO), pH / acidity +1 more | — |
| Crane Prairie Reservoir | Deschutes | D | Algal growth, Oxygen depletion (low DO), pH / acidity +1 more | — |
| Davis Lake | Deschutes | D | Oxygen depletion (low DO), pH / acidity | — |
| Crooked River Arm Lake | Jefferson | D | Algal growth, Hydrologic alteration | — |
| Lake Billy Chinook Deschutes R Arm @ Floating Station | Jefferson | D | Algal growth, Hydrologic alteration, pH / acidity | — |
| Prineville Reservoir | Crook | D | Hydrologic alteration, Mercury, Metals (other than mercury) +1 more | — |
| Siltcoos Lake | Lane | D | Algal growth | — |
| Devil'S Lake | Lincoln | D | Algal growth, Oxygen depletion (low DO), Pathogens (E. coli, fecal) | — |
| Fish Lake | Jackson | D | Algal growth, pH / acidity | — |
| Howard Prairie Lake | Jackson | D | Mercury | ✓ |
| Unity Reservoir | Baker | D | Habitat alterations, Metals (other than mercury) | ✓ |
| Phillps Lake | Baker | D | Temperature | ✓ |
| Lemolo Lake | Douglas | D | Algal growth | — |
| Ochoco Lake County Park Boat Ramp | Crook | D | Mercury, Temperature | — |
| Haystack Reservoir Campground Boat Ramp | Jefferson | D | Algal growth | — |
| Malheur Lake | Harney | F | Algal growth | — |
| Mid-Trench Lake | Klamath | F | Algal growth, Mercury, Oxygen depletion (low DO) +3 more | ✓ |
| Agency Lake South | Klamath | F | Algal growth, Oxygen depletion (low DO), pH / acidity | ✓ |
| Cullaby Lake | Clatsop | F | Algal growth, Noxious aquatic plants | — |
| Tenmile Lake | Coos | F | Algal growth, Mercury, Oxygen depletion (low DO) | ✓ |
| Brownlee Reservoir | Baker | F | Hydrologic alteration, Mercury, Temperature | — |
| Cold Springs Reservoir | Umatilla | F | Mercury | ✓ |
| Diamond Lake | Douglas | F | Algal growth, Oxygen depletion (low DO), pH / acidity | ✓ |
| Thief Valley Reservoir | Union | F | Mercury, Temperature | ✓ |
| North Tenmile Lake | Coos | NR | Algal growth, Mercury, Noxious aquatic plants +2 more | ✓ |
| Mckay Lake | Umatilla | NR | Mercury, Metals (other than mercury) | ✓ |
| Willow Creek Reservoir | Morrow | NR | Algal growth, Pathogens (E. coli, fecal) | ✓ |
| Phillips Lake | Baker | NR | Mercury, Oxygen depletion (low DO), Toxic inorganics | ✓ |
| Horse Heaven Reservoir Along East Shore | Crook | NR | Temperature | — |
| Pelican Lake | Lake | NR | Temperature | — |
| Crump Lake | Lake | NR | Temperature | — |
Frequently Asked Questions
How many lakes are impaired in Oregon?
49 of 73 graded Oregon lakes (67%) are listed as impaired in the most recent EPA ATTAINS reporting cycle. Of those, 48 are on the federal Clean Water Act §303(d) list and 22 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 Oregon?
The most common causes flagged across Oregon's impaired lakes are: Algal growth (25 lakes); Mercury (17 lakes); Temperature (17 lakes); Oxygen depletion (low DO) (13 lakes); pH / acidity (11 lakes); Hydrologic alteration (6 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 Oregon's state water-quality agency.