Polk County Lake Quality
Iowa, 11 lakes, average grade D (Nutrient-rich)
Polk County holds 11 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 8 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county-wide average grade is D — water quality issues are persistent across most of the monitored basins. 4 lakes fall into the F bracket outright.
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. Terra Park Lake (A) is the cleanest in the county.
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Quick Answers for Polk County
Planning a trip? Check special fishing regulations for Terra Park Lake — or check the official Iowa fishing regulations.
All Lakes in Polk County
11 lakes · 8 graded, 3 not rated8 graded lakes · 3 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | ATerra Park LakePolk | A | 11.5 ft | 20 µg/L | 4.7 µg/L | No recent samples | ✓ Public |
| 2 | CLake PetockaPolk | C | 3.3 ft | 39.5 µg/L | 9.3 µg/L | No recent samples | Not recorded |
| 3 | CThomas Mitchell LakePolk | C | 3.3 ft | 87 µg/L | 13.2 µg/L | No recent samples | Not recorded |
| 4 | DEaster LakePolk | D | 2.9 ft | 49.5 µg/L | 22.8 µg/L | No recent samples | ✓ Public |
| 5 | FBig Creek LakePolk | F | 2.6 ft | 80 µg/L | 35.7 µg/L | No recent samples | ✓ Public |
| 6 | FGrays LakePolk | F | 1.6 ft | 103 µg/L | 46.5 µg/L | No recent samples | ✓ Public |
| 7 | FBlue Heron LakePolk | F | 2.2 ft | 78.5 µg/L | 57.9 µg/L | No recent samples | Not recorded |
| 8 | FFort des Moines Park PondPolk | F | 2.8 ft | 68 µg/L | 32.6 µg/L | No recent samples | Not recorded |
| NRBig Creek Beach LakePolk | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRBrenton SloughPolk | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRSaylorville LakePolk | NR | No recent samples | 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
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Source: EPA National Aquatic Resource Surveys, 2026.