Lake Mallalieu
Lake Mallalieu in St. Croix County, Wisconsin has a water quality grade of D (Nutrient-rich). 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 →
- Clarity
- 2.8 ft
- Typical in August
- 74°F
- Max depth
- 17 ft
- Area
- 289 acres
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Lake Mallalieu →
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Lake Mallalieu is a 289-acre productive, nutrient-rich eutrophic lake in St. Croix County, Wisconsin with a maximum depth of 17 feet. Water quality is graded D based on 1 sampling years through 2026. 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. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyElevated nutrients
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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 2.8 ft of visibility. Phosphorus level: 53.5 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.8 ft | Not graded |
| Phosphorus | 53.5 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay 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 grade measures nutrients and algae, not lodging — cabins and rentals around Lake Mallalieu are listed below.
Top-rated places to stay near Lake Mallalieu
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 →
Water Temperature
Lake Mallalieu typically sits around 74°F at the surface in August. 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.
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 a water-quality grade. LakeQuality grades Lake Mallalieu D from EPA Water Quality Portal chemistry, 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
| Characteristic | Value |
|---|---|
| Maximum Depth | 17 ft |
| Surface Area | 289 acres |
| Public Access | Yes |
Lake Size & Watershed
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
- Campground1.3 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
Fish Species
Click a species to see every graded 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 data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.125 m/yr | 6 |
| Phosphorus | → Stable | -0.71 µg/L/yr | 7 |
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
Source: EPA ATTAINS assessment unit WI10004899 · Official waterbody report
County Ranking
Ranked #5 of 5 lakes in St. Croix County
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. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake Mallalieu?
- Lake Mallalieu in St. Croix County, Wisconsin has a water quality grade of D (Nutrient-rich). 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?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Lake Mallalieu has a water quality grade of D (Nutrient-rich). Always check local health department advisories before swimming.
What is the water temperature of Lake Mallalieu?
- Lake Mallalieu typically sits around 74°F at the surface in August, 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 a water-quality grade. LakeQuality grades Lake Mallalieu D from EPA Water Quality Portal chemistry, 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.
Are there campgrounds on Lake Mallalieu?
- Lake Mallalieu has 2 public campgrounds from USGS The National Map within 5 km, including Campground, 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
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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 Mallalieu
Other Grade D Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
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)
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
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