Decatur County Lake Quality
Iowa, 3 lakes, average grade C (Fair)
Only 3 lakes in Decatur County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. Decatur County averages to a C. The distribution behind that average matters more than the letter: a few stressed lakes versus many decent ones can produce the same average as the inverse.
The county's lakes lean shallow, which makes the grades sensitive to wind, sediment-resuspension, and any nutrient inputs from the watershed. The cleanest lake on the books is Nine Eagles Lake (A); the most-stressed is Little River Lake (F).
Quick Answers for Decatur County
Planning a trip? Check special fishing regulations for Nine Eagles Lake — or check the official Iowa fishing regulations.
All Lakes in Decatur County
| Rank | Lake | Grade | Clarity | Phosphorus |
|---|---|---|---|---|
| 1 | Nine Eagles Lake | A | 11 ft | - |
| 2 | Slipbluff Lake | B | 9 ft | - |
| 3 | Little River Lake | F | 2.3 ft | - |
Other Counties in Iowa
See how Decatur County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 15 states.
Where to stay near Decatur County
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Source: EPA National Aquatic Resource Surveys, 2026.