Diamond Lake

Diamond Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Polk County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 30 puts Diamond Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. The lake's surface area is not consistently recorded across state datasets — physical context remains partial. Diamond Lake ranks 5 of 77 in Polk County, putting it in the upper tier of locally monitored lakes.

Diamond Lake has no invasive species recorded in Wisconsin state databases as of 2020, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Diamond Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.