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LakeQuality
D

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.

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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.

MetricValueGrade
Water Clarity (Secchi Depth)2.5 ftF
Phosphorus84.9 µg/LD
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)66Eutrophic

High nutrients, frequent algae, reduced clarity

Lake Details

CharacteristicValue
Maximum Depth32 ft
Surface Area110 acres
Public AccessYes

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.

Curly-Leaf Pondweed

Water Quality Trend: Stable

Based on 6 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Declining-0.219 m/yr5
Phosphorus Improving-26.1 µg/L/yr6
See year-by-year chart →

Recreation & Access

3
Boat Landings
Yes
Public Access

Location

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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.

See full comparison →

Nearby Lakes in St. Croix County

WI DNR Lake Profile

Authoritative data from the Wisconsin DNR LakePages. 2 stations on file (most recent sample 2025).

DNR Assessment
Poor · Deep Seepage lake
Trophic State Index 69 (eutrophic) · 5-year average

Fish Species (DNR-rated)

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

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.

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

Nutrients (phosphorus, nitrogen)

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

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

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