Mahaska County Lake Quality
Wisconsin, 3 lakes, average grade F (Very Poor)
Mahaska County has 3 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. The county average is F — the most-stressed bracket in our rubric. Most monitored lakes here show persistent nutrient loading and algal pressure.
Most of the county's monitored lakes are shallow — under 50 feet — which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed. Hawthorn Lake (D) is the cleanest in the county.
Quick Answers for Mahaska County
Planning a trip? Check special fishing regulations for Hawthorn Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
All Lakes in Mahaska County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Hawthorn Lake | D | 2.4 ft | - | - |
| 2 | White Oak Lake | F | 1.4 ft | - | - |
| 3 | Lake Keomah | F | 1.5 ft | - | - |
Source: EPA National Aquatic Resource Surveys, 2026.