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.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.2 ft | D |
| Phosphorus | 129 µg/L | F |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 64 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 12 ft |
| Surface Area | 43 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.
Location
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.
- ADeer LakePolk County · mi · Two grade letters higher (D → A)
- BLoveless LakePolk County · mi · Two grade letters higher (D → B)
- BBear Trap LakePolk County · mi · Two grade letters higher (D → B)
- CLong LakePolk County · mi · Higher grade (D → C)
- CLittle Bass LakePolk County · mi · Higher grade (D → C)
Nearby Lakes in Polk County
More Wisconsin Lake Rankings
State Parks Near Mud Lake
Other Grade D Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 1 station on file (most recent sample 2020).
Fish Species (DNR-rated)
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
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
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