Updated Aug 2026
Iowa Lake Water Quality
Water quality grades for 156 of the 330 lakes we list here, across 91 counties.
Grade Distribution
All 330 Iowa lakes in the index: 156 (47.3%) carry an A–F grade and 174 (52.7%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
Top-Graded Iowa Lakes
The highest water-quality grades in Iowa — clarity, depth, and A-F grade at a glance.
Lake Map
Get Iowa water-quality updates
New grades, clarity readings, and algae advisories for Iowa lakes as samples come in. Unsubscribe anytime.
Where to stay near Iowa's top-graded lakes
Cabins, resorts, and vacation rentals around West Okoboji Lake and the other top-graded Iowa lakes pinned on the map. Live availability and prices.
Top-rated places to stay near West Okoboji Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
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Explore Iowa Lakes
Iowa reports, fishing & travel
Iowa's cleanest and most-polluted lakes, ranked A–F
Species activity outlook by water temperature and season
Where to stay at Iowa's top lakes, each with its grade
Best-graded lakes within 50 miles of Des Moines
Best-graded lakes within 50 miles of Cedar Rapids
Reservoirs in Iowa
View all 116 reservoirs →116 of 330 Iowa lakes (35%) are man-made reservoirs in the USACE National Inventory of Dams. 84 carry a High or Significant hazard rating. The oldest matched dam dates to 1900.
EPA-Impaired Lakes in Iowa
View all 132 impaired lakes →132 of 330 Iowa lakes (40%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 89 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Iowa Fishing & Recreation
Licenses, regulations, records, and where to fish across Iowa.
Counties
All 91 Iowa 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.
Iowa Lake Water Quality Dataset (2026)
Every graded Iowa lake in one spreadsheet — A–F grade, water clarity, phosphorus, chlorophyll-a, trophic state, size, public access, and a link to each lake's report card.
Top 25 Cleanest Lakes
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity | Trophic | Access |
|---|---|---|---|---|---|---|
| 1 | AWest Okoboji Lake | Dickinson | A | 15.7 ft | Mesotrophic | ✓ Public |
| 2 | ADale Maffitt Reservoir | Dallas | A | 9.8 ft | Mesotrophic | Not recorded |
| 3 | ABlue Pit Lake | Cerro Gordo | A | 17.1 ft | Mesotrophic | Not recorded |
| 4 | AAda Hayden Heritage Park Lake | Story | A | 6.8 ft | Mesotrophic | ✓ Public |
| 5 | ALittle Sioux Park Lake | Woodbury | A | 5.7 ft | Mesotrophic | Not recorded |
| 6 | ARudd Lake | Floyd | A | 8.1 ft | Mesotrophic | Not recorded |
| 7 | ASlipbluff Lake | Decatur | A | 9 ft | Mesotrophic | Not recorded |
| 8 | ALacey Keosauqua Lake | Van Buren | A | 7.1 ft | Mesotrophic | ✓ Public |
| 9 | AYenruogis Pond | Keokuk | A | 9.9 ft | Mesotrophic | Not recorded |
| 10 | ASand Lake | Marshall | A | 6.4 ft | Mesotrophic | Not recorded |
| 11 | ATerra Park Lake | Polk | A | 11.5 ft | Mesotrophic | ✓ Public |
| 12 | BStorm Lake Max Depth | Buena Vista | B | 1.7 ft | Eutrophic | ✓ Public |
| 13 | BArrowhead Lake | Sac | B | 5.6 ft | Eutrophic | ✓ Public |
| 14 | BKent Park Lake | Johnson | B | 4.8 ft | Eutrophic | Not recorded |
| 15 | BMariposa Lake | Jasper | B | 5.1 ft | Eutrophic | Not recorded |
| 16 | BMormon Trail Lake | Adair | B | 6.2 ft | Eutrophic | Not recorded |
| 17 | BNewell Pit Lake | Buena Vista | B | 4.1 ft | Eutrophic | Not recorded |
| 18 | BBob White Lake | Wayne | B | 0.6 ft | Eutrophic | ✓ Public |
| 19 | BWillow Lake | Harrison | B | 4.8 ft | Eutrophic | Not recorded |
| 20 | BPoll Miller Park Lake | Lee | B | 5.9 ft | Eutrophic | Not recorded |
| 21 | CLake Minnewashta | Dickinson | C | 2.8 ft | Eutrophic | ✓ Public |
| 22 | CUpper Gar Lake | Dickinson | C | 3.9 ft | Eutrophic | ✓ Public |
| 23 | CRailroad Lake | Scott | C | 5.1 ft | Eutrophic | Not recorded |
| 24 | CBig Spirit Lake | Dickinson | C | 5.5 ft | Eutrophic | ✓ Public |
| 25 | CMitchell Lake | Black Hawk | C | 2.3 ft | Eutrophic | ✓ Public |
25 Lakes Needing Attention
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | FOkamanpeedan Lake | Emmet | F | 1 ft |
| 2 | FHumeston Reservoir | Wayne | F | 1.6 ft |
| 3 | FCorydon Reservoir | Wayne | F | 1.9 ft |
| 4 | FLake Fisher | Davis | F | 2 ft |
| 5 | FAlice Wyth Lake | Black Hawk | F | 1.6 ft |
| 6 | FTerry Trueblood Lake | Johnson | F | 1.1 ft |
| 7 | FVolga Lake | Fayette | F | 2.1 ft |
| 8 | FLake Pahoja | Lyon | F | 1.7 ft |
| 9 | FPierce Creek Lake | Page | F | 2.2 ft |
| 10 | FBlue Lake | Monona | F | 0.9 ft |
| 11 | FLittle River Lake | Decatur | F | 2.3 ft |
| 12 | FWindmill Lake | Taylor | F | 2.5 ft |
| 13 | FViking Lake | Montgomery | F | 3.3 ft |
| 14 | FLake Hendricks | Howard | F | 1.5 ft |
| 15 | FLake Sugema | Van Buren | F | 2.3 ft |
| 16 | FSmith Lake | Kossuth | F | 2.4 ft |
| 17 | FIngham Lake | Emmet | F | 1.4 ft |
| 18 | FIndian Lake | Van Buren | F | 1.2 ft |
| 19 | FWilliamson Pond Max Depth | Lucas | F | 1.6 ft |
| 20 | FThayer Lake | Union | F | 3.5 ft |
| 21 | FBrowns Lake | Woodbury | F | 0.7 ft |
| 22 | FLake Geode | Des Moines | F | 2.1 ft |
| 23 | FLake of Three Fires Max Depth | Taylor | F | 2 ft |
| 24 | FArbor Lake Max Depth | Poweshiek | F | 1.3 ft |
| 25 | FFogle Lake | Ringgold | F | 2.3 ft |
156 of the 330 Iowa lakes in this index carry an A–F water-quality grade, spread over 91 counties. Those grades rest on measurements from the Iowa Department of Natural Resources, 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. A-grade lakes are scarce among the Iowa lakes that carry a letter: about 7% of them. Most sit in C or D, productive, often shallow, frequently algal in late summer.
By surface area the largest lake here is Rathbun Lake, at about 11,013 acres, and 24 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. A meaningful share of the state's graded lakes register as hypereutrophic: heavily nutrient-loaded, frequent blooms, low summer transparency. These are usually shallow, surrounded by row-crop agriculture, with little volume to buffer the inputs. The cleanest county on average is Floyd (grade A); the most-stressed is Davis. The gap between the top and bottom counties is large enough that a single figure for Iowa lake water quality hides real local variation.
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.