Iosco County Lake Quality
Michigan, 6 lakes, average grade B (Good)
Only 6 lakes in Iosco 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. With an average grade of B, Iosco County sits comfortably above the Michigan median.
A meaningful share of Iosco's lakes break 50 feet of depth, which matters because deep lakes hold cooler water all summer and resist the resuspended-sediment problems that plague shallow basins. The county's best-graded lake is Long Lake (A).
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Quick Answers for Iosco County
Planning a trip? Check special fishing regulations for Long Lake — or check the official Michigan fishing regulations.
Fishing in Iosco County
All Lakes in Iosco County
6 lakes · 3 graded, 3 not rated3 graded lakes · 3 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Max Depth | Access |
|---|---|---|---|---|---|---|---|---|
| 1 | ALong LakeIosco | A | 14 ft | 14 µg/L | 1 µg/L | No recent samples | 62 ft | Not recorded |
| 2 | AChain LakesIosco | A | 12.5 ft | 10.5 µg/L | 1.4 µg/L | No recent samples | No recent samples | Not recorded |
| 3 | CVan Etten LakeIosco | C | 6 ft | 34 µg/L | 6.9 µg/L | No recent samples | No recent samples | Not recorded |
| NRLittle Island LakeIosco | NR | 7 ft | No recent samples | No recent samples | No recent samples | 9 ft | ✓ Public | |
| NRLoon LakeIosco | NR | 23 ft | No recent samples | No recent samples | No recent samples | 128 ft | ✓ Public | |
| NRCedar LakeIosco | NR | 12 ft | 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 Michigan
See how Iosco County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 49 states and 2 Canadian provinces.
Source: EPA National Aquatic Resource Surveys, 2026.