Upper Prior Lake

Upper Prior Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

At a TSI of 53, Upper Prior Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. At 50 ft of maximum depth, Upper Prior Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. The lake's 386 acres and 6.2 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Within Scott County's 17 graded lakes, Upper Prior Lake ranks 9 — below the local median, though not at the bottom.

Upper Prior Lake is on the Minnesota infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. The fishery includes walleye alongside the lake's other 16 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. Ice-out has been logged at Upper Prior Lake more than two dozen times, putting the median around Apr 5 — a useful baseline for tracking climate trends. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.