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F

Calhoun County Lake Quality

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

Only 1 lakes in Calhoun 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.

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. North Twin Lake (F) is the cleanest in the county.

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All Lakes in Calhoun County

RankLakeGradeClarityPhosphorus
1North Twin LakeF1.1 ft-

See how Calhoun 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.