Lake Dubay
Lake Dubay in Marathon County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 64.9 µg/L. Surface area: 7800 acres.
- Clarity
- 2.5 ft
- Max depth
- ~101 ft est.
- Area
- 7,800 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- 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 Dubay →
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Lake Dubay is a 7,800-acre productive, nutrient-rich eutrophic lake in Marathon County, Wisconsin with an estimated average depth of about 101 feet. Water quality is graded D based on 1 sampling years through 2026. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 6 public boat landings. Compared to the 3 other monitored lakes in Marathon County, Lake Dubay ranks #4 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 2.5 ft of visibility. Phosphorus level: 64.9 µg/L. Trophic State Index: 64.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | Not graded |
| Phosphorus | 64.9 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 64 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Lake Dubay
Compare lakeside cabins, hotels, and vacation rentals near Lake Dubay in Marathon 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 Dubay are listed below.
Top-rated places to stay near Lake Dubay
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Planning a trip? Cabins and lodging at Lake Dubay → · more Wisconsin lake trips
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Lake Dubay covering fish populations, stocking, water quality, and management. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Lake DuBay comprehensive survey 2022Comprehensive Survey · WI DNR (PDF)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~101 ft est. |
| Average Depth | ~28 ft est. |
| Surface Area | 7,800 acres |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Wisconsin has not published bathymetry for Lake Dubay.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Du Bay ParkPublic
- South DrivePublic
- Highway CPublic
- Lake Du Bay DamSemi-private
- Lake Du BaySemi-private
- Seagull DriveSemi-private
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Lake Dubay
Water Quality Trend: ↓ Declining
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.001 m/yr | 6 |
| Phosphorus | ↓ Declining | +5.83 µg/L/yr | 6 |
Reservoir Info (USACE NID)
Lake Dubay is a man-made reservoir impounded by the Dubay (completed 1942), built primarily for hydroelectric on the Wisconsin River; concrete-type dam, 40 ft tall and 8,630 ft long.
- Surface area
- 7,800 ac
- Normal storage
- 128,000 ac-ft
- Max storage
- 128,800 ac-ft
- Drainage area
- 4,822 sq mi
- Hazard class
- High
- Owner
- Consolidated Water Power Company
All listed purposes: Hydroelectric;Flood Risk Reduction.
Source: USACE National Inventory of Dams, NID ID WI00784 · Operator website
EPA Impairment Status
Lake Dubay 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 WI10027538 · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Lake Dubay under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Mullins Cheese IncKnowlton Tn · 1.3 mi away · NPDES WI0054127Recent violation
- Ephraim Wastewater Treatment FacilityEphraim · 3.7 mi away · NPDES WI0061271Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #4 of 4 lakes in Marathon County
Nearby Lakes With Higher Grades
Lake Dubay holds Grade D. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Marathon County
Frequently asked questions about Lake Dubay
Where is Lake Dubay?
- Lake Dubay is a lake in Marathon 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 Dubay?
- Lake Dubay in Marathon County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 64.9 µg/L. Surface area: 7800 acres.
Is Lake Dubay 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 Dubay has a water quality grade of D (Nutrient-rich). Always check local health department advisories before swimming.
How deep is Lake Dubay?
- No published bathymetric survey covers Lake Dubay, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 101 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 7800 acres.
Are there boat ramps on Lake Dubay?
- Lake Dubay has 6 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Du Bay Park, South Drive, Highway C, Lake Du Bay Dam, among others. Public access is listed as yes.
Explore Lake Dubay 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 Marathon County
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its grade
Lakes in the Wisconsin River 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 Dubay
Other Grade D Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Where this data comes from
58 measurements from 2 monitoring stations, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX58 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (2)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory