Lake St Croix
Lake St Croix in St. Croix County, Wisconsin has a water quality grade of B (Good). Water clarity: 5.6 ft visibility. Phosphorus: 30 µg/L. Maximum depth: 60 ft. Surface area: 7696 acres.
Wisconsin DNR lists Smallmouth Bass as common on Lake St Croix. DNR survey details →
- Clarity
- 5.6 ft
- Typical in August
- 78°F
- Max depth
- 60 ft
- Area
- 7,696 acres
- Type
- Eutrophic
- Public access
- Yes
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Lake St Croix is a 7,696-acre productive, nutrient-rich eutrophic lake in St. Croix County, Wisconsin with a maximum depth of 60 feet. Water quality is graded B based on 1 sampling years through 2020. The lake supports 7 documented fish species including Musky, Largemouth Bass, and Smallmouth Bass. Public access is available with 1 public boat landing and 6 public beaches. Compared to the 4 other monitored lakes in St. Croix County, Lake St Croix ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2020-09-10. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyBacteria C
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Based on E. coli testing, Lake St Croix occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 5.6% of 18 samples across 8 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Wisconsin’s current beach and health-department advisories before swimming.
Water Quality Grade: B (Good)
Murky, only visible to about 5.6 ft. Phosphorus level: 30 µg/L. Trophic State Index: 53.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.6 ft | Not graded |
| Phosphorus | 30 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 53 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Lake St Croix
Compare lakeside cabins, hotels, and vacation rentals near Lake St Croix in St. Croix County, Wisconsin — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Lake St Croix
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Planning a trip? Cabins and lodging at Lake St Croix → · more Wisconsin lake trips
Water Temperature
Lake St Croix typically sits around 78°F at the surface in August. Summer average is about 76°F. Usually warmest in Jul (about 78°F) and coldest in May (about 59°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 73 field readings (2011–2019) via the EPA Water Quality Portal. See the full Lake St Croix water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Lake St Croix — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (55,976 cells/mL) on July 18, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR lists Smallmouth Bass as common on Lake St Croix.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Lake St Croix B from EPA Water Quality Portal chemistry. Catch rate is not a swim clearance and is not a weekly bite report.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 3 stations on file (most recent sample 2023).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Lake St Croix covering fish populations, stocking, water quality, and management. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —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)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 60 ft |
| Surface Area | 7,696 acres |
| Public Access | Yes |
Recreation & Access
- South Cove RoadPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
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.
EPA Impairment Status
Lake St Croix 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 WI10025187 · Official waterbody report · Matched by proximity (0.3 km)
County Ranking
Ranked #1 of 5 lakes in St. Croix County
Nearby Lakes in St. Croix County
Frequently asked questions about Lake St Croix
Where is Lake St Croix?
- Lake St Croix is a lake in St. Croix County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake St Croix?
- Lake St Croix in St. Croix County, Wisconsin has a water quality grade of B (Good). Water clarity: 5.6 ft visibility. Phosphorus: 30 µg/L. Maximum depth: 60 ft. Surface area: 7696 acres.
Is Lake St Croix safe to swim in?
- Based on E. coli testing, Lake St Croix occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 5.6% of 18 samples across 8 seasons. That works out to a bacteria swim-safety grade of C — a historical summary of past testing, not a current reading. Lake St Croix has a water quality grade of B (Good). Bacteria levels can spike quickly after heavy rain, so always check Wisconsin's current beach and health-department advisories before you swim.
What is the water temperature of Lake St Croix?
- Lake St Croix typically sits around 78°F at the surface in August, from 73 EPA Water Quality Portal field readings (2011–2019). That is a typical value for the month, not a live reading.
How deep is Lake St Croix?
- Lake St Croix has a maximum depth of 60 feet. The lake covers 7696 acres.
What fish are in Lake St Croix?
- Fish species found in Lake St Croix include Musky, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye, Sturgeon, Catfish. Lake St Croix is located in St. Croix County, Wisconsin.
What did the DNR fisheries survey find at Lake St Croix?
- Wisconsin DNR lists Smallmouth Bass as common on Lake St Croix. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Lake St Croix B from EPA Water Quality Portal chemistry. Catch rate is not a swim clearance and is not a weekly bite report.
Does Lake St Croix have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Lake St Croix (clouds, ice, or an off-season gap). The most recent reading was moderate (55,976 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Are there boat ramps on Lake St Croix?
- Lake St Croix has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include South Cove Road. Public access is listed as yes.
Explore Lake St Croix across LakeQuality
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Wisconsin
Fish species and best lakes in St. Croix County
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its grade
Lakes in the St. Croix Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Wisconsin's cleanest and most-polluted lakes, ranked
More Wisconsin Lake Rankings
State Parks Near Lake St Croix
Other Grade B Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Where this data comes from
6 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Minnesota Water Science Center
USGS-MN6 samples · 2020
Analytical methods
- Secchi disk method
- P, wu, WCA, persulfate CF color
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory