Jasper County Lake Quality
Iowa, 3 lakes, average grade C (Fair)
Jasper County has 3 monitored 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. 2 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. Jasper 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 Mariposa Lake (B); the most-stressed is Rock Creek Max Depth Lake (F).
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Quick Answers for Jasper County
Planning a trip? Check special fishing regulations for Mariposa Lake — or check the official Iowa fishing regulations.
All Lakes in Jasper County
3 lakes · 2 graded, 1 not rated2 graded lakes · 1 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | BMariposa LakeJasper | B | 5.1 ft | 31 µg/L | 8.9 µg/L | No recent samples | Not recorded |
| 2 | FRock Creek Max Depth LakeJasper | F | 1.1 ft | 167.5 µg/L | 107.5 µg/L | No recent samples | Not recorded |
| NRRock Creek Beach LakeJasper | NR | 1.1 ft | No recent samples | No recent samples | No recent samples | ✓ Public |
NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
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Other Counties in Iowa
See how Jasper County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..
Source: EPA National Aquatic Resource Surveys, 2026.