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LakeQuality
Late afternoon sun over Slim Lake, scattering a bright path across wind-textured water
D

Hardin County Lake Quality

Illinois, 1 lake, average grade D (Nutrient-rich)

Hardin County holds 1 monitored lake. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. Every one of those lake carries an A–F grade, so the county-level summary covers the full set rather than a monitored subset. The county-wide average grade is D — water quality issues are persistent across most of the monitored basins. 0 lakes fall into the F bracket outright.

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 Tecumseh Lake (D); the most-stressed is Tecumseh Lake (D).

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All Lakes in Hardin County

1 lake1 graded lake

#LakeGradeClarityPhosphorusAlgaeTrophicAccess
1DTecumseh LakeHardinD3.6 ft27 µg/L22.5 µg/LNo recent samplesNot recorded

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See how Hardin 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.