Updated Aug 2026
Iowa Lake Water Quality
Water quality grades for 209 monitored lakes across 76 counties.
Across Iowa, 209 lakes carry an active water-quality grade spread over 76 counties. The underlying measurements come from the Iowa Department of Natural Resources, alongside federal programs and volunteer monitoring networks. A-grade lakes are scarce in Iowa: about 6% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
A meaningful share of the state's monitored 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 Pottawattamie. The gap between the top and bottom counties is large enough that "Iowa lake water quality" hides real local variation.
Grade Distribution
All 209 Iowa lakes in the index: 164 (78.5%) carry an A–F grade and 45 (21.5%) are not rated, because they lack enough recent nutrient or algae sampling to support a letter.
Where to stay near Iowa
Top-rated places to stay near Iowa
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Top-Graded Iowa Lakes
The highest water-quality grades in Iowa — clarity, depth, and A-F grade at a glance.
Lake Map
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 123 reservoirs →123 of 209 Iowa lakes (59%) are man-made reservoirs in the USACE National Inventory of Dams. 91 carry a High or Significant hazard rating. The oldest matched dam dates to 1900.
EPA-Impaired Lakes in Iowa
View all 149 impaired lakes →149 of 209 Iowa lakes (71%) are officially listed as impaired under Clean Water Act §303(d) in the most recent EPA ATTAINS reporting cycle. 102 have an approved Total Maximum Daily Load (TMDL) restoration plan.
Iowa Fishing & Recreation
Licenses, regulations, records, and where to fish across Iowa.
Counties
All 76 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 | ANine Eagles Lake | Decatur | A | 11 ft | Mesotrophic | ✓ Public |
| 6 | ALittle Sioux Park Lake | Woodbury | A | 5.7 ft | Mesotrophic | Not recorded |
| 7 | ARudd Lake | Floyd | A | 8.1 ft | Mesotrophic | Not recorded |
| 8 | ASlipbluff Lake | Decatur | A | 9 ft | Mesotrophic | Not recorded |
| 9 | ALacey Keosauqua Lake | Van Buren | A | 7.1 ft | Mesotrophic | ✓ Public |
| 10 | AYenruogis Pond | Keokuk | A | 9.9 ft | Mesotrophic | Not recorded |
| 11 | ASand Lake | Marshall | A | 6.4 ft | Mesotrophic | Not recorded |
| 12 | ATerra Park Lake | Polk | A | 11.5 ft | Mesotrophic | ✓ Public |
| 13 | BStorm Lake Max Depth | Buena Vista | B | 1.7 ft | Eutrophic | ✓ Public |
| 14 | BArrowhead Lake | Sac | B | 5.6 ft | Eutrophic | ✓ Public |
| 15 | BKent Park Lake | Johnson | B | 4.8 ft | Eutrophic | Not recorded |
| 16 | BMariposa Lake | Jasper | B | 5.1 ft | Eutrophic | Not recorded |
| 17 | BMormon Trail Lake | Adair | B | 6.2 ft | Eutrophic | Not recorded |
| 18 | BNewell Pit Lake | Buena Vista | B | 4.1 ft | Eutrophic | Not recorded |
| 19 | BBob White Lake | Wayne | B | 0.6 ft | Eutrophic | ✓ Public |
| 20 | BWillow Lake | Harrison | B | 4.8 ft | Eutrophic | Not recorded |
| 21 | BLake Wapello | Davis | B | 7.5 ft | Eutrophic | ✓ Public |
| 22 | BPoll Miller Park Lake | Lee | B | 5.9 ft | Eutrophic | Not recorded |
| 23 | CLake Minnewashta | Dickinson | C | 2.8 ft | Eutrophic | ✓ Public |
| 24 | CUpper Gar Lake | Dickinson | C | 3.9 ft | Eutrophic | ✓ Public |
| 25 | CRailroad Lake | Scott | C | 5.1 ft | Eutrophic | Not recorded |
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 |
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
The top-graded lake in every state we cover, picked grade-first with water clarity as the tie-breaker — plus the states whose winner is still not clean.
State-by-state Secchi champions: the clearest measured lake in each U.S. state we grade, which is not the same as the cleanest nutrient grade.
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.