
McDonough County Lake Quality
Illinois, 5 lakes, average grade F (Algae-prone)
McDonough County holds 5 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 1 of those lake 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 Vermont City Lake (F); the most-stressed is Vermont City Lake (F).
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Quick Answers for McDonough County
Planning a trip? Check special fishing regulations for Vermont City Lake — or check the official Illinois fishing regulations.
All Lakes in McDonough County
5 lakes · 1 graded, 4 not rated1 graded lake · 4 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | FVermont City LakeMcDonough | F | No recent samples | 130.5 µg/L | 45.8 µg/L | No recent samples | Not recorded |
| NRVermont New LakeMcDonough | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRColmar LakeMcDonough | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRSpring LakeMcDonough | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRArgyle LakeMcDonough | 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 Illinois
See how McDonough 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.