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D

Mud Lake

Polk County, WisconsinEutrophic

Mud Lake pulls a D on the LakeGrade rubric — phosphorus loading and limited clarity hold it below the Wisconsin average. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

At a TSI of 64, Mud Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. At only 12 ft deep, Mud Lake is shallow — wind keeps the water column mixed and sediment resuspension drives phosphorus levels harder to manage. The lake is compact at 43 acres, with partial shoreline records and little volume to buffer nutrient inputs. Mud Lake ranks 69 of 74 in Polk County — at the lower end of the locally monitored distribution.

An invasive species record — Chinese Mystery Snail — has been logged at Mud Lake; Wisconsin DNR maintains the official infested-waters list. The fishery is bass-led, with 3 documented species across the lake's records. 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 2020-09-09. Grade methodology: LakeGrade methodology.

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Swimming Safety

Swimming not recommended, poor water quality with high algae risk

Water Quality Grade: D, Poor

Murky, only visible to about 5.2 ft. Phosphorus level: 129 µg/L. Trophic State Index: 64.

MetricValueGrade
Water Clarity (Secchi Depth)5.2 ftD
Phosphorus129 µg/LF
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)64Eutrophic

High nutrients, frequent algae, reduced clarity

Lake Details

CharacteristicValue
Maximum Depth12 ft
Surface Area43 acres

Fish Species

Click a species to see every graded lake where it is documented.

→ 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 & Introduced Species

Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.

Chinese Mystery Snail

Location

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County Ranking

Ranked #69 of 74 lakes in Polk County

Cleaner Lakes Within 30 Miles

Mud Lake holds Grade D. 5 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Polk County

WI DNR Lake Profile

Authoritative data from the Wisconsin DNR LakePages. 1 station on file (most recent sample 2020).

Fish Species (DNR-rated)

Panfish(Present)Largemouth Bass(Present)Northern Pike(Present)

EPA Impairment Status

Mud Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5R).

Causes of impairment

Nutrients (phosphorus, nitrogen)

Source: EPA ATTAINS assessment unit WI10004974 · Official waterbody report

Data Sources

Water quality data from the EPA Water Quality Portal

Impairment status from EPA ATTAINS 303(d) database

Grading methodology based on Metropolitan Council standards

Fish and recreation data from Wisconsin DNR Lakes

Most recent sample: 2020-09-09

Monitoring stations: 1

Where to stay near Mud Lake

Compare lakeside cabins, hotels, and vacation rentals near Mud Lake in Polk County, Wisconsin — live availability and prices for your trip.

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