St. Croix County Lake Quality

St. The county-level average smooths over real differences — a single agricultural watershed near the southwest corner can pull the average down even if the rest of the county runs clean. 4 of those lakes carry recent nutrient and algae readings. The county-level summary describes that subset, not every water body listed. The county's readings sit in the middle of the Wisconsin range, with one or two lakes pulling the average up or down depending on year.

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 St Croix has the lowest nutrient and algae readings in the county.