Marion County Lake Quality
Illinois, 10 lakes, average grade F (Algae-prone)
Marion County has 10 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. 6 of those lakes carry an A–F grade. The county-level summary describes that subset, not every water body listed. The county average is F — the most-stressed bracket in our rubric. Most monitored lakes here show persistent nutrient loading and algal pressure.
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 Salem Lake (F); the most-stressed is Salem Lake (F).
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Quick Answers for Marion County
Planning a trip? Check special fishing regulations for Salem Lake — or check the official Illinois fishing regulations.
All Lakes in Marion County
10 lakes · 6 graded, 4 not rated6 graded lakes · 4 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | FSalem LakeMarion | F | 1 ft | 234 µg/L | 77.5 µg/L | No recent samples | ✓ Public |
| 2 | FForbes LakeMarion | F | 1.4 ft | 140.5 µg/L | 75.9 µg/L | No recent samples | ✓ Public |
| 3 | FCentralia LakeMarion | F | 1.5 ft | 132 µg/L | 69.7 µg/L | No recent samples | ✓ Public |
| 4 | FRaccoon LakeMarion | F | 1.2 ft | 285 µg/L | 73.5 µg/L | No recent samples | ✓ Public |
| 5 | FKinmundy Old LakeMarion | F | 1.5 ft | 277 µg/L | 114.8 µg/L | No recent samples | Not recorded |
| 6 | FKinmundy New LakeMarion | F | 2.9 ft | 49.5 µg/L | 38 µg/L | No recent samples | ✓ Public |
| NRLake CentraliaMarion | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRForbes LakeMarion | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRSalem ReservoirMarion | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRC and EI ReservoirMarion | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded |
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 Illinois
See how Marion 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.