Lake Mallalieu
St. Croix County, Wisconsin289 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Lake Mallalieu. Here is what has been measured.
- Eutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- 2 aquatic invasives
- 17 ft max depth
- Public access
Lake Mallalieu in St. Croix County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 2.8 ft visibility. Phosphorus: 53.5 µg/L. Maximum depth: 17 ft. Surface area: 289 acres.
Wisconsin DNR lists Largemouth Bass as common on Lake Mallalieu. DNR survey details →
Lake Mallalieu is a 289-acre productive, nutrient-rich eutrophic lake in St. Croix County, Wisconsin with a maximum depth of 17 feet. Overall water quality is improving over recent sampling years. The lake supports 4 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Public access is available with 1 public boat landing. Compared to the 4 other monitored lakes in St. Croix County, Lake Mallalieu ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-15. Methodology: how these readings are compared.
Lake Mallalieu covers about 290 acres in St. Croix County. It has one public boat landing. Vrbo is where to look for cabins and lake homes around Lake Mallalieu, and Booking.com and Expedia search hotels near the lake for your dates.
What Lake Mallalieu is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
- Fishing4 species recorded
- Camping1 public campground nearby
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.
Nutrient and algae readings are not a swimming clearance. Lake Mallalieu is listed impaired under Clean Water Act §303(d) (IR 5R) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Lake Mallalieu 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 Mallalieu
These are the measurements Wisconsin DNR publishes for Lake Mallalieu, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 2.8 ft of visibility. Phosphorus 53.5 µg/L. TSI 62.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 2.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 53.5µg/L | Poor 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. | 62 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Lake Mallalieu
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Lake Mallalieu typically sits around 49°F at the surface in October. Summer average is about 74°F. Usually warmest in Jul (about 77°F) and coldest in Mar (about 48°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (48°F) to its warmest (77°F).
Typical surface water temperature by month, from 30 field readings (2024–2025) via the EPA Water Quality Portal. See the full Lake Mallalieu water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Lake Mallalieu — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (33,113 cells/mL) on March 20, 2021.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR lists Largemouth Bass as common on Lake Mallalieu.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Lake Mallalieu’s water-quality measurements separately, and the water-quality trend over 7 years of monitoring is improving. 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. Monitored by volunteers since 2004. 3 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
Max depth
17 ft
Surface area
289 acres
Public access
Yes
Listed by Wisconsin DNR
Lake Size & Watershed
Watershed (drainage) area
296 sq mi
HydroLAKES / HydroSHEDS
Shoreline
4.4 mi
HydroLAKES / HydroSHEDS
Elevation
682 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Lake MallalieuPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Public campgrounds near Lake Mallalieu
- Campground1.2 km
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
Stays via Stay22
Stays near Lake Mallalieu
Compare lakeside cabins, hotels, and vacation rentals near Lake Mallalieu 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Lake Mallalieu are listed below.
Top-rated places to stay near Lake Mallalieu
Prices for Oct 9–11, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Follow Lake Mallalieu’s readings
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Fish Species
Click a species to see every lake where it is documented.
Fishing Lake Mallalieu
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: Improving
Based on 7 years of monitoring (2020–2026).
Water clarity
Improving6 years
Phosphorus
Stable-0.71 µg/L/yr7 years
Reservoir Info (USACE NID)
Lake Mallalieu is a man-made reservoir impounded by the Lower Power (completed 1866), built primarily for recreation on the Willow River; gravity-type dam, 22 ft tall and 400 ft long.
- Surface area
- 270 ac
- Normal storage
- 1,388 ac-ft
- Max storage
- 3,000 ac-ft
- Drainage area
- 175 sq mi
- Hazard class
- Low
- Owner
- City of Hudson
Source: USACE National Inventory of Dams, NID ID WI00187 · Operator website · Matched by proximity (0.2 km)
EPA Impairment Status
Lake Mallalieu is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5R).
Causes of impairment
Designated uses not supporting: Aquatic life, Recreation.
Source: EPA ATTAINS assessment unit WI10004899 · Official waterbody report
Nearby Lakes in St. Croix County
Frequently asked questions about Lake Mallalieu
Where is Lake Mallalieu?
- Lake Mallalieu 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 Mallalieu?
- Lake Mallalieu in St. Croix County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 2.8 ft visibility. Phosphorus: 53.5 µg/L. Maximum depth: 17 ft. Surface area: 289 acres.
Is Lake Mallalieu safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake Mallalieu is listed impaired under Clean Water Act §303(d) (IR 5R) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Lake Mallalieu?
- Lake Mallalieu typically sits around 49°F at the surface in October, from 30 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Lake Mallalieu?
- Lake Mallalieu has a maximum depth of 17 feet. The lake covers 289 acres.
What fish are in Lake Mallalieu?
- Fish species found in Lake Mallalieu include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike. Lake Mallalieu is located in St. Croix County, Wisconsin.
What did the DNR fisheries survey find at Lake Mallalieu?
- Wisconsin DNR lists Largemouth Bass as common on Lake Mallalieu. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Lake Mallalieu’s water-quality measurements separately, and the water-quality trend over 7 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
Does Lake Mallalieu have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Lake Mallalieu (clouds, ice, or an off-season gap). The most recent reading was moderate (33,113 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 Mallalieu?
- Lake Mallalieu has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Lake Mallalieu. Public access is listed as yes.
Can I fish at Lake Mallalieu?
- Lake Mallalieu 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.
Are there campgrounds on Lake Mallalieu?
- Lake Mallalieu has 1 public campground from USGS The National Map within 5 km, including Campground. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
Explore Lake Mallalieu across LakeQuality
Depth, room, public access, and the state wake-sport rules
4.4 mi away · 45 ft
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
91 measurements from 1 monitoring station, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX91 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory
Public campgrounds from USGS The National Map Structures, within about 3 miles