Upper Estuary Lake

On the scoring rubric Upper Estuary Lake grades a D: clarity at 1.9 ft and 49 µg/L of phosphorus keep it in the lower bracket for St. Louis County. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Minnesota norms.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. Upper Estuary Lake is unusually deep for Minnesota at 55 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 10,255 acres, Upper Estuary Lake is one of the larger lakes in St. Louis County, with 195.5 miles of shoreline supporting multiple distinct use patterns. Within the 215 graded lakes of St. Louis County, Upper Estuary Lake sits at rank 200, near the bottom of the county list.

Upper Estuary Lake has no invasive species recorded in Minnesota state databases as of 2025, though prevention practices still apply at all access points. Upper Estuary Lake's fishery is anchored by muskellunge, with 33 documented species in total — a destination water for muskie anglers. Public access is available — the lake is on the Minnesota PCA public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.