
Montgomery County Lake Quality
Illinois, 8 lakes, average grade F (Algae-prone)
Montgomery County holds 8 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. 2 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 Glenn Shoals Lake (F); the most-stressed is Glenn Shoals Lake (F).
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Quick Answers for Montgomery County
Planning a trip? Check special fishing regulations for Glenn Shoals Lake — or check the official Illinois fishing regulations.
All Lakes in Montgomery County
8 lakes · 2 graded, 6 not rated2 graded lakes · 6 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | FGlenn Shoals LakeMontgomery | F | 1 ft | 122 µg/L | 72.1 µg/L | No recent samples | ✓ Public |
| 2 | FLou Yaeger LakeMontgomery | F | 1.8 ft | 255 µg/L | 72.6 µg/L | No recent samples | ✓ Public |
| NRCoffeen LakeMontgomery | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRLake HillsboroMontgomery | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRLake Glenn ShoalsMontgomery | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRFivemile LakeMontgomery | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRLake Lou YaegerMontgomery | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRWalton LakeMontgomery | 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 Montgomery 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.