What is the water quality grade for Decorah Lake?

Decorah Lake in Juneau County, Wisconsin received a water quality grade of F (Very Poor). Phosphorus: 116 µg/L. Maximum depth: 15 ft. Surface area: 314 acres.

Is Decorah Lake safe to swim in?

Avoid swimming, very poor water quality, potential algae toxins. Decorah Lake has an overall water quality grade of F. Always check local health department advisories before swimming.

How deep is Decorah Lake?

Decorah Lake has a maximum depth of 15 feet. The lake covers 314 acres.

What fish are in Decorah Lake?

Fish species found in Decorah Lake include Panfish, Largemouth Bass, Northern Pike, Walleye. Decorah Lake is located in Juneau County, Wisconsin.

Decorah Lake

Juneau County, WisconsinLimited DataHypereutrophic

Decorah Lake earns an F: 116 µg/L of phosphorus and clarity readings still being added signal heavy nutrient loading from the surrounding watershed.

A TSI above 70 puts Decorah Lake in hypereutrophic territory: visible blooms are common, and clarity rarely climbs even in early summer. A maximum depth of 15 ft puts Decorah Lake in the middle of Wisconsin's depth distribution. At 314 acres, Decorah Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Within the 2 graded lakes of Juneau County, Decorah Lake sits at rank 2, near the bottom of the county list.

Decorah Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. Walleye are documented at Decorah Lake, one of 4 fish species on record for the lake. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.

Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2021-08-23. Grade methodology: LakeGrade methodology.

Reviewed by LakeQuality Editorial Team · Updated May 31, 2026