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LakeQuality
C

Mud Lake

Jefferson County, WisconsinEutrophic

Mud Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

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. A maximum depth of 22 ft puts Mud Lake in the middle of Wisconsin's depth distribution. At 84 acres, Mud Lake sits below the Wisconsin median: a small water where shoreline activity has an outsized effect on water quality. Mud Lake ranks 7 of 8 in Jefferson County — at the lower end of the locally monitored distribution.

Mud Lake has at least one documented invasive species (Curly-Leaf Pondweed), so boaters and anglers should observe clean-drain-dry steps when leaving the lake. The lake's fish records list 2 species — a varied community without one dominant gamefish. 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 2025-08-25. Grade methodology: LakeGrade methodology.

Swimming Safety

Generally safe for swimming, moderate water quality

Water Quality Grade: C, Fair

Moderate clarity, visible to about 7.4 ft. Phosphorus level: 63.1 µg/L. Trophic State Index: 56.

MetricValueGrade
Water Clarity (Secchi Depth)7.4 ftC
Phosphorus63.1 µg/LD
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)56Eutrophic

High nutrients, frequent algae, reduced clarity

Lake Details

CharacteristicValue
Maximum Depth22 ft
Surface Area84 acres

Fish Species

Click a species to see all Wisconsin and Minnesota lakes where it is found.

→ Best fishing times for Mud Lake (14-day solunar calendar)

→ Is it safe to eat fish from Mud Lake? (mercury & PFAS guide)

Mud Lake fishing regulations (limits, seasons, special rules)

Invasive Species

Curly-Leaf Pondweed

Water Quality Trend: Improving

Based on 7 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Improving+0.049 m/yr7
Phosphorus Improving-5.01 µg/L/yr5

Location

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County Ranking

Ranked #7 of 8 lakes in Jefferson County

Nearby Lakes in Jefferson County

Eutrophic Lakes in Wisconsin

WI DNR Lake Profile

Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2017. 1 station on file (most recent sample 2026).

DNR Assessment
Poor · Deep Lowland lake
Trophic State Index 70 (eutrophic) · 5-year average

Fish Species (DNR-rated)

Panfish(Common)Northern Pike(Present)

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Fish and recreation data from Wisconsin DNR Lakes

Most recent sample: 2025-08-25

Monitoring stations: 1