St. Croix County Lake Quality
Wisconsin, 7 lakes, average grade C (Fair)
St. Croix County has 7 graded lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. The county average is C — the middle of the rubric, with one or two lakes pulling the average up or down depending on year.
Many of the county's lakes are deep glacial basins — over 50 feet at their deepest point — which gives them thermal stratification and a buffer against summer warming. Bass Lake (grade A) is the cleanest in the county.
Quick Answers for St. Croix County
Planning a trip? Check special fishing regulations for Bass Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Wisconsin regulations index.
DNR Reports (9)
Wisconsin DNR Fisheries Survey resources for lakes in St. Croix County. browse all reports →
- 2025Cedar Lake comprehensive spring survey, 2025Comprehensive Survey · WI DNR · 2025 (PDF)
- 2025Hatfield Lake spring shocking survey, 2025Spring Shocking Survey · WI DNR · 2025 (PDF)
- 2025Lake George spring survey, 2025Fisheries Survey · WI DNR · 2025 (PDF)
- 2025Little Falls Lake spring shocking survey, 2025Spring Shocking Survey · WI DNR · 2025 (PDF)
- 2025Twin Lakes northern pike stocking assessment survey, 2025Fisheries Survey · WI DNR · 2025 (PDF)
- 2024Apple Lake spring survey, 2024Fisheries Survey · WI DNR · 2024 (PDF)
- 2021Cedar Lake spring survey, 2021Fisheries Survey · WI DNR · 2021 (PDF)
- —Population assessment of lake sturgeon in the upper St. Croix River, Minnesota and Wisconsin 2003-2011Fisheries Survey · WI DNR (PDF)
- —St. Croix River catfish survey, 2020-2024Fisheries Survey · WI DNR (PDF)
All Lakes in St. Croix County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Bass Lake | A | 31.2 ft | - | 14 µg/L |
| 2 | Bass Lake Pump Site | A | 29.6 ft | 33 ft | 14.5 µg/L |
| 3 | Lake St. Croix | B | 5.6 ft | 60 ft | 16.5 µg/L |
| 4 | Lake Mallalieu | C | 9 ft | 17 ft | 54.4 µg/L |
| 5 | Apple Lake | C | 7.4 ft | 32 ft | 84.9 µg/L |
| 6 | St. Croix Lake | D | 5.1 ft | 60 ft | - |
| 7 | St. Croix Lake | D | 4.4 ft | 60 ft | - |
Source: EPA National Aquatic Resource Surveys, 2026.