Sioux County Lake Quality

Sioux 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 recent nutrient and algae readings, so the county-level summary covers the full set rather than a monitored subset. Most monitored lakes in Sioux County are productive, shallow basins; each lake page shows its own phosphorus and chlorophyll-a readings beside the EPA condition class.

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. Froelich Dam Lake has the lowest nutrient and algae readings in the county.