PlainLakes

State water-quality picture · #24 by reported lake-type waterbodies

Colorado lakes and reservoirs

Every figure on this page is computed from the assessment decisions Colorado reported to the U.S. Environmental Protection Agency under Clean Water Act sections 303(d) and 305(b) (reporting cycles 1996–2024), plus daily water-level observations from the U.S. Geological Survey.

344
Reported waterbodies
89
Not supporting a use
Not reported
Fish use assessments
8
Gauged lakes

Colorado in one line

344 lake-type waterbodies in Colorado are reported to EPA ATTAINS across reporting cycles 1996–2024: 89 assessed as not supporting at least one designated use, 74 fully supporting, and 181 without a definitive overall verdict. The most-listed impairment cause is Arsenic, on 39 waterbodies.

344
reported waterbodies
89
not supporting a use
74
fully supporting
55%
of definitive verdicts impaired

An unassessed waterbody is neither confirmed clean nor confirmed impaired; states assess on multi-year cycles.

Colorado pairs a mid-pack inventory with a denser USGS gauge link-set

8 gauge-linked lakes put Colorado in the upper third of states on that link count, against a mid-third register of 344 units.

Data updated 2026-08-17

According to the U.S. Environmental Protection Agency's ATTAINS program, Colorado reported 344 lake-type waterbodies in Colorado in the August 2026 extract. See our methodology for filer attribution and multi-year reporting cycles.

Overall-status mix on Colorado's mid-size inventory

Every reported lake-type unit in Colorado falls into exactly one overall-status bucket. This bar is the inventory partition; the cause chart and national gauge below answer different questions.

Most-listed impairment causes in Colorado

Waterbodies carrying each listed cause, most first

waterbodies

What this shows Arsenic is the most-listed impairment cause in Colorado, on 39 of the lake-type waterbodies reported there.

Source EPA ATTAINS As of Reporting cycles 1987–2026
55 N

Computed share from EPA ATTAINS filed records, not an official EPA rating or safety grade.

Share of Colorado waterbodies with a verdict on fish, recreation, aquatic life or drinking water assessed as not supporting a use

Colorado: 55% of ruled verdicts are not-supporting, against a national share of 53%, 1.0× the national rate.

Reporting practice

Colorado's definitive-verdict share, by the numbers

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.

Colorado holds the 24th-largest reported lake-type inventory in the country, 344 assessment units, carrying a definitive verdict on 47.4% of it. The counts above describe the 163 units carrying a verdict, not all 344 reported. Colorado has also retired 56 lake-type assessment units, superseded filings that are kept on the site but not counted here.

The states reporting at the nearest rates are Washington (47.2%) and North Carolina (50.8%).

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.

Colorado against every comparable state

Share of reported lake-type waterbodies carrying a definitive verdict

47.4% 34th of 47 higher than 13 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 Colorado

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 John Martin Reservoir. Not Supporting 17,147
2 Blue Mesa Reservoir Fully Supporting 8,957
3 Lake Granby. Not Supporting 7,036
4 Two Buttes Reservoir, Two Buttes Pond, Hasty Lake, Holbrook Reservoir, Burchfield Lake, Nee-Skah (Queens) Reservoir, Neeso Pah Reservoir, Nee Noshe Reservoir. Fully Supporting 6,123
5 Lake and reserviors tributary to the South Platte River Not Assessed 5,770
6 Lake Meredith. Not Supporting 5,531
7 Adobe Creek Reservoir. Not Supporting 4,784
8 Prewitt Reservoir, Empire Reservoir, and Vancil Reservoir. Fully Supporting 4,529
9 Pueblo Reservoir. Not Supporting 4,264
10 McPhee Reservoir. Not Supporting 4,030
11 Riverside Reservoir Fully Supporting 3,705
12 Lake San Cristobal, Taylor Park Reservoir, Morrow Point Reservoir, Crystal Reservoir, and Silver Jack Reservoir. Fully Supporting 3,672

By cause count

Most-listed waterbodies in Colorado

Waterbodies carrying the most listed impairment causes among the lake-type units reported by Colorado.

# Waterbody Listed causes
1 Duck Lake Not Supporting 4
2 Barker Reservoir. Not Supporting 3
2 Barr Lake. Not Supporting 3
2 Berkeley Lake Not Supporting 3
2 DeWeese Reservoir. Not Supporting 3
2 Horseshoe Lake (Lake Meriam) Not Supporting 3
2 Milton Reservoir. Not Supporting 3
2 Terrace Reservoir. Not Supporting 3
2 Trinidad Reservoir. Not Supporting 3
10 Adobe Creek Reservoir. Not Supporting 2

8 of the 10 rows in this table tie on the ranked value: 8 at 3 (rank 2). 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 Colorado

Lakes with a linked USGS gauge and a daily water-level record. Readings are daily-batch snapshots, not real-time.

Where Colorado sits nationally on scale vs. impaired share

Assessed-corpus size does not predict impaired share: a state with a large register can still post a low not-supporting rate, and a small register can post a high one.

Source: EPA ATTAINS, states above the sample floor 2×2 strategic matrix plotting 36 entities by Definitive verdicts (assessed corpus) (X) and Impaired share (%) (Y), with a crosshair dividing the plot into four quadrants. Large corpus, high shareSmall corpus, high shareLarge corpus, low shareSmall corpus, low share 01,0002,0003,0004,0005,000 0%20%40%60%80%100%120% Definitive verdicts (assessed corpus) Impaired share (%) New Hampshire · 2,783, 100%Washington · 393, 100%New Jersey · 604, 96.5%Massachusetts · 718, 94.4%Oregon · 178, 92.7%California · 224, 90.2%New York · 642, 87.7%Illinois · 497, 87.3%Rhode Island · 140, 85%Oklahoma · 195, 78.5%Virginia · 231, 78.4%South Dakota · 186, 78%Kansas · 316, 76.3%Iowa · 203, 67.5%Florida · 1,003, 63.4%Nebraska · 352, 62.2%Indiana · 241, 60.2%North Carolina · 152, 59.2%Utah · 134, 57.5%Missouri · 267, 56.6%Kentucky · 129, 55.8%Colorado · 163, 54.6%ColoradoMinnesota · 3,364, 53.4%Arkansas · 117, 53%Alabama · 273, 52.4%Georgia · 119, 39.5%South Carolina · 540, 39.3%Michigan · 2,339, 34.5%Connecticut · 139, 31.7%North Dakota · 176, 29.5%Texas · 433, 28.9%Pennsylvania · 516, 26.2%Vermont · 712, 21.6%Idaho · 237, 21.5%Wisconsin · 4,718, 10.4%Maine · 303, 10.2%
Source: EPA ATTAINS, states above the sample floor
NameDefinitive verdicts (assessed corpus)Impaired share (%)
New Hampshire2,783100%
Washington393100%
New Jersey60496.5%
Massachusetts71894.4%
Oregon17892.7%
California22490.2%
New York64287.7%
Illinois49787.3%
Rhode Island14085%
Oklahoma19578.5%
Virginia23178.4%
South Dakota18678%
Kansas31676.3%
Iowa20367.5%
Florida1,00363.4%
Nebraska35262.2%
Indiana24160.2%
North Carolina15259.2%
Utah13457.5%
Missouri26756.6%
Kentucky12955.8%
Colorado (this record)16354.6%
Minnesota3,36453.4%
Arkansas11753%
Alabama27352.4%
Georgia11939.5%
South Carolina54039.3%
Michigan2,33934.5%
Connecticut13931.7%
North Dakota17629.5%
Texas43328.9%
Pennsylvania51626.2%
Vermont71221.6%
Idaho23721.5%
Wisconsin4,71810.4%
Maine30310.2%
Source: EPA ATTAINS, states above the sample floor

The crosshair sits at the median across the 36 qualifying states on each axis, not the range midpoint, so it splits the group evenly. Colorado is highlighted.

States with similar inventory scale or impairment load

Two EPA ATTAINS peer sets outside Colorado. The reporting-practice chart above stays on definitive-verdict share; these neighborhoods are cross-state nearest neighbors on register size and not-supporting counts.

Comparable register size

Nearest states by lake-type units on the register (344 here).

Similar not-supporting load

Nearest states by units assessed not supporting a use (89 here). Inventory peers above are omitted.

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: 47.4% of the inventory reported from Colorado carries a definitive verdict, 34th 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 Colorado 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 Colorado 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 Colorado, 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.