Apple Lake
St. Croix County, WisconsinEutrophic
Apple Lake pulls a D on the LakeGrade rubric — phosphorus loading and limited clarity hold it below the Wisconsin average. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.
Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. A maximum depth of 32 ft puts Apple Lake in the middle of Wisconsin's depth distribution. Apple Lake covers 110 acres alongside partial shoreline records — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Apple Lake ranks 5 of 5 in St. Croix County — at the lower end of the locally monitored distribution.
Apple 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 fishery includes walleye alongside the lake's other 4 documented species — a notable draw for Wisconsin anglers. A documented public access point at Apple Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. 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 2026-04-22. Grade methodology: LakeGrade methodology.
Watch Apple Lake water quality
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 2.5 ft of visibility. Phosphorus level: 84.9 µg/L. Trophic State Index: 66.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | F |
| Phosphorus | 84.9 µg/L | D |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 66 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 32 ft |
| Surface Area | 110 acres |
| Public Access | Yes |
Fish Species
Click a species to see every graded lake where it is documented.
→ Best fishing times for Apple Lake (14-day solunar calendar)
→ Is it safe to eat fish from Apple Lake? (mercury & PFAS guide)
→ Apple 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.
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.219 m/yr | 5 |
| Phosphorus | ↑ Improving | -26.1 µg/L/yr | 6 |
Recreation & Access
Location
County Ranking
Ranked #5 of 5 lakes in St. Croix County
Cleaner Lakes Within 30 Miles
Apple Lake holds Grade D. 5 nearby lakes hold higher grades.
- ALower Pine LakePolk County · mi · Two grade letters higher (D → A)
- APine LakePolk County · mi · Two grade letters higher (D → A)
- APaulsen LakePolk County · mi · Two grade letters higher (D → A)
- AChurch Pine LakePolk County · mi · Two grade letters higher (D → A)
- ABass LakeSt. Croix County · mi · Two grade letters higher (D → A)
Nearby Lakes in St. Croix County
More Wisconsin Lake Rankings
State Parks Near Apple Lake
Other Grade D Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 2 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Apple Lake covering fish populations, stocking, water quality, and management. 1 report on file.
- 2024Apple Lake spring survey, 2024Fisheries Survey · WI DNR · 2024 (PDF)
EPA Impairment Status
Apple Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit WI10005074 · 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
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2026-04-22
Monitoring stations: 1
Where to stay near Apple Lake
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