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F

McDonough County Lake Quality

Illinois, 1 lakes, average grade F (Very Poor)

Only 1 lakes in McDonough County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. 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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All Lakes in McDonough County

RankLakeGradeClarityPhosphorus
1Vermont City LakeF-103 µg/L

See how McDonough County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 15 states.

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Source: EPA National Aquatic Resource Surveys, 2026.