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

Lyon County Lake Quality

Iowa, 1 lake, average grade F (Algae-prone)

Lyon County has 1 monitored lake — 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. 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 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. Lake Pahoja (F) is the cleanest in the county.

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Where to stay near Lyon County

Top-rated places to stay near Lyon County

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All Lakes in Lyon County

1 lake1 graded lake

#LakeGradeClarityPhosphorusAlgaeTrophicAccess
1FLake PahojaLyonF1.7 ft218 µg/L44.8 µg/LNo recent samples✓ Public

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See how Lyon 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.