Some of these decisions are EPA's. 25 of these 1,431 records carry a Clean Water Act cleanup plan EPA established rather than Oregon. They are counted in every figure on this page, and each record page names which.
State water-quality picture · #8 by reported lake-type waterbodies
Oregon lakes and reservoirs
Every figure on this page is computed from the assessment decisions Oregon reported to the U.S. Environmental Protection Agency under Clean Water Act sections 303(d) and 305(b) (reporting cycles 1998–2024), plus daily water-level observations from the U.S. Geological Survey.
- 1,431
- Reported waterbodies
- 165
- Not supporting a use
- 90
- Fish use not supporting
- 20
- Gauged lakes
Oregon in one line
1,431 lake-type waterbodies in Oregon are reported to EPA ATTAINS across reporting cycles 1998–2024: 165 assessed as not supporting at least one designated use, 14 fully supporting, and 1,252 without a definitive overall verdict. The most-listed impairment cause is Temperature, on 80 waterbodies.
- 1,431
- reported waterbodies
- 165
- not supporting a use
- 14
- fully supporting
- 93%
- of definitive verdicts impaired
An unassessed waterbody is neither confirmed clean nor confirmed impaired; states assess on multi-year cycles. 1 of those 14 fully supporting verdicts (7%) rest on designated uses this site does not report (irrigation, navigation and industrial water supply), with Oregon recording no verdict on fish consumption, recreation, aquatic life and drinking water. They are counted above because the state filed them, and excluded from the impaired share below because that figure compares states.
Oregon's large register still carries a heavy not-supporting share
Among the largest third of state lake-type registers (1,431 units), Oregon also sits in the upper third for ruled not-supporting share (93%). The size and the load move together here, not every large inventory does.
Data updated 2026-08-17
According to the U.S. Environmental Protection Agency's ATTAINS program, Oregon reported 1,431 lake-type waterbodies in Oregon in the August 2026 extract. See our methodology for filer attribution and multi-year reporting cycles.
How Oregon's large inventory splits across overall status
Each of the 1,431 lake-type units reported by Oregon lands in exactly one overall-status bucket. On a register this large, the bar is an inventory partition, the cause chart and national gauge below answer different questions.
Most-listed impairment causes in Oregon
Waterbodies carrying each listed cause, most first
- Temperature
Temperature
80 waterbodies
- Methylmercury
Methylmercury
54 waterbodies
- Harmful Algal Blooms
Harmful Algal Blooms
45 waterbodies
- Dissolved Oxygen 31
Dissolved Oxygen
31 waterbodies
- Chlorophyll-a 23
Chlorophyll-a
23 waterbodies
What this shows Temperature is the most-listed impairment cause in Oregon, on 80 of the lake-type waterbodies reported there.
Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.
Oregon: 93% of ruled verdicts are not-supporting, against a national share of 53%, 1.8× the national rate.
Reporting practice
Oregon's inventory: still mostly without a definitive verdict
Each reporting authority decides how much of the water it files to EPA it actually assesses in a cycle. That decision sets the denominator behind every count on this page.
Oregon holds the 8th-largest reported lake-type inventory in the country, 1,431 assessment units, carrying a definitive verdict on 12.4% of it. The counts above describe the 178 units carrying a verdict, not all 1,431 reported. Oregon has also retired 4 lake-type assessment units, superseded filings that are kept on the site but not counted here.
The state reporting at the nearest rate is Indiana (15.2%).
Assessing more of an inventory is a reporting choice, set by cycle length, monitoring budget and how finely a state splits its waters into units. It is not a measure of water quality, and it is why a raw count from one state does not sit beside a raw count from another. How assessment coverage varies.
Oregon against every comparable state
Share of reported lake-type waterbodies carrying a definitive verdict
12.4% 47th of 47 the lowest of 47 states
the 47 comparable states, by definitive-verdict share
Each bar is a band; taller bars hold more states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA ATTAINS · Reporting cycles 1987–2026
Each bar counts states whose definitive-verdict share falls in that 10-point band. The 47 states shown are those reporting at least 25 lake-type units; a share off a smaller inventory is precision the data does not have.
By size
Largest assessed lakes in Oregon
By assessed acreage as reported in ATTAINS. Acreage is the assessed unit's size, which can differ from a lake's full surface area.
| # | Waterbody | Assessed acres |
|---|---|---|
| 1 | Goose Lake Not reported | 93,152 |
| 2 | Malheur Slough Not Supporting | 73,544 |
| 3 | Upper Klamath Lake Not Supporting | 62,130 |
| 4 | Columbia River Assessment unit OR_LK_1708000605_04_100320 Not Supporting | 55,630 |
| 5 | Lake Abert Not Assessed | 44,751 |
| 6 | Summer Lake Not reported | 31,606 |
| 7 | Harney Lake Not reported | 31,369 |
| 8 | Columbia River Assessment unit OR_LK_1708000605_04_107234 Not Supporting | 15,437 |
| 9 | Sutton Creek Not reported | 15,017 |
| 10 | Columbia River Assessment unit OR_LK_1708000605_04_100323 Not Supporting | 14,845 |
| 11 | <Null> Not reported | 13,212 |
| 12 | Brownlee Reservoir Not Supporting | 12,530 |
By cause count
Most-listed waterbodies in Oregon
Waterbodies carrying the most listed impairment causes among the lake-type units reported by Oregon.
| # | Waterbody | Listed causes |
|---|---|---|
| 1 | Brownlee Reservoir Not Supporting | 10 |
| 2 | Oxbow Reservoir Not Supporting | 9 |
| 3 | Columbia River Assessment unit OR_LK_1708000605_04_100323 Not Supporting | 8 |
| 3 | Columbia River Assessment unit OR_LK_1708000605_04_100320 Not Supporting | 8 |
| 5 | Columbia River Assessment unit OR_LK_1708000605_04_107234 Not Supporting | 7 |
| 5 | Upper Klamath Lake Not Supporting | 7 |
| 7 | Columbia River Assessment unit OR_LK_1707010106_88_100132 Not Supporting | 6 |
| 7 | Columbia River Assessment unit OR_LK_1707010504_88_100138 Not Supporting | 6 |
| 7 | Hells Canyon Reservoir Not Supporting | 6 |
| 7 | Lake Owyhee Not Supporting | 6 |
8 of the 10 rows in this table tie on the ranked value: 2 at 8 (rank 3), 2 at 7 (rank 5), 4 at 6 (rank 7). Tied rows share a rank and are listed in no meaningful order; where a tie reaches the top the medal is shared, because nothing separates those rows.
Gauge network
Lakes with a daily level record in Oregon
Lakes with a linked USGS gauge and a daily water-level record. Readings are daily-batch snapshots, not real-time.
- Upper Klamath Lake Not Supporting USGS gauge 11505800 Level record →
- Lake Abert Not Assessed USGS gauge 10387150 Level record →
- Agency Lake Not Supporting USGS gauge 11504300 Level record →
- Fern Ridge Lake Not Supporting USGS gauge 14168000 Level record →
- Lookout Point Lake Not Supporting USGS gauge 14149000 Level record →
- Detroit Lake Not Supporting USGS gauge 14180500 Level record →
- Green Peter Lake Not Supporting USGS gauge 14186100 Level record →
- Lost Creek Lake Not Supporting USGS gauge 14335040 Level record →
- Diamond Lake Not Supporting USGS gauge 14312450 Level record →
- Hills Creek Lake Not Supporting USGS gauge 14145100 Level record →
- Fall Creek Lake Not Supporting USGS gauge 14150900 Level record →
- Dorena Lake Not Supporting USGS gauge 14155000 Level record →
States near Oregon's heavier not-supporting load
Two EPA ATTAINS peer sets outside Oregon. The reporting-practice chart above stays on definitive-verdict share; the neighborhoods below emphasize cross-state nearest neighbors when the not-supporting count is in the upper third.
Similar reported inventory
Nearest states by lake-type units on the register (1,431 here).
- Florida · 1,475 units · 44 off
- Indiana · 1,588 units · 157 off
- Massachusetts · 1,191 units · 240 off
- Washington · 832 units · 599 off
Peers are nearest-neighbor matches on EPA ATTAINS register size and not-supporting counts among states with at least 25 reported units. Impairment peers skip states already listed in the inventory column so the two link sets stay distinct.
Using this state picture
- Comparisons across states hold on shares, not counts: 12.4% of the inventory reported from Oregon carries a definitive verdict, 47th of 47 comparable states. National rankings
- Fish-consumption verdicts here are assessment decisions. Species-level meal advice comes from the state fish-advisory program. Consumption guide
- Browse every named Oregon waterbody with a populated record. Browse waterbodies
PlainLakes renders state assessment decisions and federal gauge observations without modification.
Figures on this page are computed from the assessment decisions Oregon reported to EPA's ATTAINS system and from USGS National Water Information System daily values, no number is typed in by an editor. State counts aggregate every lake-type assessment unit reported by Oregon, including unnamed units that never receive their own page. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-08-17. Primary sources: EPA ATTAINS and USGS National Water Information System.