Updated August 2026
Cleanest Lakes in Iowa: Top 25 Ranked by Water Quality
Ranked from the Iowa lakes with enough nutrient and algae sampling to compare. Lakes with fewer than three sampling years, and lakes nobody has sampled, are not ranked here.
The single cleanest lake in Iowa is West Okoboji Lake, ranked first on its measured clarity and nutrients in the 2026 sampling record. Cleanliness here is measured by Secchi depth (clarity), total phosphorus, and chlorophyll-a — all sourced from EPA Water Quality Portal and state agency sampling, shown as reported. The full top 25 ranked list appears below.
The "cleanest" ranking on LakeQuality is built from the measured nutrients and algae — phosphorus and chlorophyll-a read against EPA National Lakes Assessment 2022 ecoregion classes. Secchi clarity is shown and used only as a tiebreak. The cleanest Iowa lake on the current data is West Okoboji Lake.
The top of the cleanest-lakes list is dominated by deep, glacial, cold-water basins — the same basins that carry the lowest nutrient readings overall. The pattern is not coincidence: depth and watershed land-use are the dominant inputs to water-clarity and nutrient-loading both.
| Rank | Lake | County | Clarity | Phosphorus | Chlorophyll-a | Area |
|---|---|---|---|---|---|---|
| 1 | West Okoboji Lake | Dickinson | 15.7 ft | 20 µg/L | 2.3 µg/L | - |
| 2 | Dale Maffitt Reservoir | Dallas | 9.8 ft | 20 µg/L | 2.1 µg/L | 230 acres |
| 3 | Blue Pit Lake | Cerro Gordo | 17.1 ft | 20 µg/L | 2.4 µg/L | - |
| 4 | Ada Hayden Heritage Park Lake | Story | 6.8 ft | 19 µg/L | 5.2 µg/L | - |
| 5 | Little Sioux Park Lake | Woodbury | 5.7 ft | 19 µg/L | 5.7 µg/L | - |
| 6 | Rudd Lake | Floyd | 8.1 ft | 14 µg/L | 4.5 µg/L | - |
| 7 | Slipbluff Lake | Decatur | 9 ft | 17.5 µg/L | 4.5 µg/L | 18 acres |
| 8 | Lacey Keosauqua Lake | Van Buren | 7.1 ft | 21.5 µg/L | 4.7 µg/L | 23 acres |
| 9 | Yenruogis Pond | Keokuk | 9.9 ft | 21 µg/L | 6.2 µg/L | - |
| 10 | Sand Lake | Marshall | 6.4 ft | 25 µg/L | 3.6 µg/L | - |
| 11 | Terra Park Lake | Polk | 11.5 ft | 20 µg/L | 4.7 µg/L | - |
| 12 | Storm Lake Max Depth | Buena Vista | 1.7 ft | 123.5 µg/L | 11 µg/L | - |
| 13 | Arrowhead Lake | Sac | 5.6 ft | 26 µg/L | 7.1 µg/L | 110 acres |
| 14 | Kent Park Lake | Johnson | 4.8 ft | 25 µg/L | 11.4 µg/L | 29 acres |
| 15 | Mariposa Lake | Jasper | 5.1 ft | 31 µg/L | 8.9 µg/L | 19 acres |
| 16 | Mormon Trail Lake | Adair | 6.2 ft | 25 µg/L | 9.7 µg/L | 33 acres |
| 17 | Newell Pit Lake | Buena Vista | 4.1 ft | 37 µg/L | 11.9 µg/L | - |
| 18 | Bob White Lake | Wayne | 0.6 ft | 264 µg/L | 10.1 µg/L | 104 acres |
| 19 | Willow Lake | Harrison | 4.8 ft | 35 µg/L | 9.5 µg/L | 19 acres |
| 20 | Poll Miller Park Lake | Lee | 5.9 ft | 28 µg/L | 7.7 µg/L | 15 acres |
| 21 | Lake Minnewashta | Dickinson | 2.8 ft | 47 µg/L | 19 µg/L | - |
| 22 | Upper Gar Lake | Dickinson | 3.9 ft | 52.5 µg/L | 13.1 µg/L | - |
| 23 | Railroad Lake | Scott | 5.1 ft | 44.5 µg/L | 8.3 µg/L | 29 acres |
| 24 | Big Spirit Lake | Dickinson | 5.5 ft | 55 µg/L | 16.3 µg/L | - |
| 25 | Mitchell Lake | Black Hawk | 2.3 ft | 40.5 µg/L | 18.7 µg/L | - |
Get updates when Iowa's cleanest-lake list changes
New nutrient and algae samples can move a lake up or down this ranking. Unsubscribe anytime.
Clearest lakes in Iowa by water clarity
“Clearest” ranks by Secchi depth — how far you can see into the water — which can differ from the combined cleanliness score above. The clearest water in Iowa is Blue Pit Lake at 17.1 ft of Secchi visibility.
- 1. Blue Pit Lake — 17.1 ft, Cerro Gordo County
- 2. West Okoboji Lake — 15.7 ft, Dickinson County
- 3. Terra Park Lake — 11.5 ft, Polk County
- 4. Yenruogis Pond — 9.9 ft, Keokuk County
- 5. Dale Maffitt Reservoir — 9.8 ft, Dallas County
Frequently Asked Questions
What is the cleanest lake in Iowa?
West Okoboji Lake ranks first on measured clarity and nutrients in the 2026 Iowa sampling record. Each lake's nutrient and algae readings — total phosphorus, total nitrogen, chlorophyll-a, and turbidity — are shown beside the EPA National Lakes Assessment 2022 condition class for that lake's own ecoregion, so a reading is compared against the lakes it would naturally resemble. LakeQuality publishes no letter grade. Cleanliness here means a low nutrient load and little algae, measured directly from EPA and state DNR samples; where two lakes tie on nutrients and algae, the deeper Secchi reading ranks first.
Where in Iowa has the cleanest water?
Iowa's clearest waters are concentrated in deeper, lower-nutrient glacial basins with forested or low-agriculture watersheds. Among the current top-ranked lakes above, counties like Dickinson, Buena Vista, and Dallas produce the highest-scoring lakes.
What is the clearest lake in Iowa?
Blue Pit Lake is the clearest lake in Iowa by water clarity, with a Secchi depth of 17.1 feet — the deepest transparency in our 2026 dataset. "Clearest" ranks by Secchi depth (how far you can see into the water) specifically, while "cleanest" combines clarity with phosphorus and chlorophyll-a. See our full clearest-lakes ranking for Iowa for the top 25 by Secchi clarity.
Are these lakes safe to swim in?
Not on these readings alone. Clarity and nutrient readings are not a swimming clearance: they do not measure E. coli, cyanotoxins, or a posted beach closure, and a lake with low chlorophyll-a can still bloom. Always check current posted advisories before swimming: water quality changes seasonally, especially in late summer when blue-green algae bloom risk peaks.
How is this ranking calculated?
Lakes are ranked on phosphorus, chlorophyll-a and clarity as measured by EPA and state agency sampling, read against EPA National Lakes Assessment 2022 condition classes for that lake’s ecoregion, not a Iowa-only 0–100 average. Water clarity is shown beside the nutrient readings. Lakes with limited sampling do not headline the table.
What are the top 5 cleanest lakes in the US?
There is no single national ranking of cleanest lakes — each state agency uses different metrics. Crater Lake (Oregon) is widely cited as the clearest US lake, with Secchi depths over 30 m. Lake Tahoe and Lake Superior are also top-tier nationally. Within Iowa, the 25 lakes ranked above have the lowest nutrient and algae readings in our 2026 dataset.
How we rank cleanest lakes
Cleanliness here means three things working together:
- Secchi clarity — how deep you can see into the water (in feet). Greater depth = clearer water = lower suspended sediment and algae.
- Total phosphorus — the nutrient that fuels algae. Lower phosphorus levels mean less algae growth potential.
- Chlorophyll-a — the green pigment in algae. Direct measurement of how much algae is currently in the water.
Each signal is normalized against Iowa state norms and combined into a single 0–100 score. The lakes above are sorted by that combined score.Full methodology →
More on clean water
How nutrient and algae readings are read against EPA ecoregion condition classes, what each class means in the water, and why a clean reading is not a clearance.
The cleanest U.S. lakes under 500 acres, ranked on measured nutrients, algae, and water clarity — with the size cutoff applied to the lake, not the sample.
A practical checklist for picking a lake with good water quality — clarity, phosphorus, algae history, depth, and the data to check before you commit.
Where to stay near Iowa's cleanest lakes
Compare cabins, resorts, and rentals around West Okoboji Lake and the other lakes in this ranking, with live availability and prices for your trip. Each pin on the map is one of the ranked lakes above.
Top-rated places to stay near West Okoboji Lake
Prices for Oct 30–Nov 1, 4 adults. Change dates on the map below.
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Source: EPA National Aquatic Resource Surveys, 2026.