Cass County Lake Quality
Illinois, 6 lakes — no lake here has enough monitoring data for a grade
Cass County has 6 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. No lake in Cass County has enough sampling behind it for an A–F grade yet. The 6 monitored lakes below carry whatever clarity, phosphorus, and chlorophyll-a measurements exist.
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.
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Top-rated places to stay near Cass County
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Quick Answers for Cass County
Planning a trip? Check special fishing regulations for Boujan Swale Lake — or check the official Illinois fishing regulations.
All Lakes in Cass County
6 lakes · 0 graded, 6 not rated0 graded lakes · 6 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| NRBoujan Swale LakeCass | NR | No recent samples | No recent samples | 136 µg/L | No recent samples | ✓ Public | |
| NRFinger LakeCass | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRMeyers PondCass | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRSwamp SloughCass | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRSangamon BayCass | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NREagle LakeCass | 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.
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Other Counties in Illinois
See how Cass 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.