Lake St Croix
St. Croix County, Wisconsin7,696 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Lake St Croix. Here is what has been measured.
- Eutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- 3 aquatic invasives
- 60 ft max depth
- Public access
- Limited data
Lake St Croix in St. Croix County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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 →
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. 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. Methodology: how these readings are compared.
What Lake St Croix is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
- Beach6 documented beaches
- Fishing7 species recorded
- Deep water60 ft surveyed max depth
- Big water7,696 acres
Swimming conditions
Readings onlyRecreation use not supported
Based on clarity and algae readings from past sampling — there is no 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.
Whether Lake St Croix is safe to swim in today is a call for the Wisconsin Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Lake St Croix
These are the measurements Wisconsin DNR publishes for Lake St Croix, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.6 ft. Phosphorus 30 µg/L. TSI 53.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 30µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 53 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Lake St Croix
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Lake St Croix typically sits around 65°F at the surface in October. 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.
Column height runs from this lake’s coldest month (59°F) to its warmest (78°F).
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 water quality. LakeQuality shows Lake St Croix’s water-quality measurements separately. 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
Max depth
60 ft
Surface area
7,696 acres
Public access
Yes
Listed by Wisconsin DNR
Recreation & Access
- South Cove RoadPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays 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
Follow Lake St Croix’s readings
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Fish Species
Click a species to see every 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
Designated uses not supporting: Aquatic life, Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit WI10025187 · Official waterbody report
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. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Lake St Croix?
- Lake St Croix in St. Croix County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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 is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Lake St Croix is safe to swim in today is a call for Wisconsin's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of Lake St Croix?
- Lake St Croix typically sits around 65°F at the surface in October, 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 water quality. LakeQuality shows Lake St Croix’s water-quality measurements separately. 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.
Can I fish at Lake St Croix?
- Lake St Croix has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Wisconsin's fish and wildlife agency, so check its current regulations before you go.
Explore Lake St Croix across LakeQuality
Depth, room, public access, and the state wake-sport rules
Fish species and the cleanest 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 readings
Lakes in the St. Croix Watershed, ranked by water quality
Wisconsin's cleanest lakes, ranked on agency measurements
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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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from 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