Pierce County, Minnesota · Water Quality Report Card
Lake St Croix
Lake St Croix in Pierce County, Minnesota has a water quality grade of B (Good). Water clarity: 7.2 ft visibility. Phosphorus: 32.5 µg/L. Maximum depth: 78 ft. Surface area: 8393.04 acres.
- Clarity
- 7.2 ft
- Max depth
- 78 ft
- Area
- 8,393 acres
- Type
- Eutrophic
- Trend
- → Stable
- Public access
- No
Lake St Croix is a 8,393-acre productive, nutrient-rich eutrophic lake in Pierce County, Minnesota with a maximum depth of 78 feet. Water quality is graded B based on 1 sampling years through 2023. Water clarity is improving over recent sampling years. The lake supports 36 documented fish species including bigmouth buffalo, black bullhead, and black crappie. No public access — the lake is private or restricted.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-10-05. Grade methodology: LakeGrade methodology.
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
Moderate clarity, visible to about 7.2 ft. Phosphorus level: 32.5 µg/L. Trophic State Index: 51.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7.2 ft | |
| Phosphorus | 32.5 µg/L | Good |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 51 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 78 ft |
| Surface Area | 8,393 acres |
| Shoreline Length | 124.5 mi |
| Public Access | No |
Where to stay near Lake St Croix
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Fish Species
Click a species to see every graded lake where it is documented.
Fishing Lake St Croix
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 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.084 m/yr | 5 |
| Phosphorus | ↓ Declining | +7.2 µg/L/yr | 5 |
Location
County Ranking
Ranked #1 of 1 lakes in Pierce County
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Explore Lake St Croix across LakeGrade
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More records, surveys & data sources
Where this data comes from
15 measurements from 2 monitoring stations, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Minnesota Water Science Center
USGS-MN10 samples · 2020 - Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA5 samples · 2023
Analytical methods
- Secchi disk method
- P, wu, WCA, persulfate CF color
- Field measurement/observation, generic method
Monitoring station identifiers (2)
Grade thresholds come from the U.S. EPA National Lakes Assessment 2022 Technical Support Document (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated.
Data Sources
Water quality data from the EPA Water Quality Portal
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion
Lake details from Minnesota DNR LakeFinder
Most recent sample: 2023-10-05
Monitoring stations: 2