Rock Island County Lake Quality
Illinois, 3 lakes, average grade C (Fair)
Rock Island County has 3 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. 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 C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.
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. George Lake (C) is the cleanest in the county.
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Quick Answers for Rock Island County
Planning a trip? Check special fishing regulations for George Lake — or check the official Illinois fishing regulations.
All Lakes in Rock Island County
3 lakes · 1 graded, 2 not rated1 graded lake · 2 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| 1 | CGeorge LakeRock Island | C | 4.2 ft | 40.5 µg/L | 17 µg/L | No recent samples | ✓ Public |
| NRBowles SloughRock Island | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRLake GeorgeRock Island | 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 Rock Island 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.