Mason Lake
Mason Lake in Adams County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 1.1 ft visibility. Phosphorus: 105 µg/L. Maximum depth: 9 ft. Surface area: 882 acres.
- Clarity
- 1.1 ft
- Typical in August
- 76°F
- Max depth
- 9 ft
- Area
- 882 acres
- Type
- Hypereutrophic
- 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 Mason Lake →
Next lake in Adams County
Mason Lake is a 882-acre highly nutrient-loaded hypereutrophic lake in Adams County, Wisconsin with a maximum depth of 9 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 5 documented fish species including Musky, Panfish, and Largemouth Bass. Public access is available with 4 public boat landings. Compared to the 17 other monitored lakes in Adams County, Mason Lake ranks #17 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-29. Grade methodology: LakeGrade 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 1.1 ft of visibility. Phosphorus level: 105 µg/L. Trophic State Index: 73.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.1 ft | Not graded |
| Phosphorus | 105 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 73 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Mason Lake
Compare lakeside cabins, hotels, and vacation rentals near Mason Lake in Adams 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 Mason Lake are listed below.
Top-rated places to stay near Mason Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Mason Lake typically sits around 76°F at the surface in August. Summer average is about 76°F. Usually warmest in Jul (about 79°F) and coldest in May (about 69°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 20 field readings (2024–2026) via the EPA Water Quality Portal. See the full Mason Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 9 ft |
| Surface Area | 882 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Big SloughPublic
- Mason Lake - NorthPublic
- Mason Lake - SouthPublic
- Mason Lake - EastPublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Mason Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1993. 2 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Water Quality Trend: ↑ Improving
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.07 m/yr | 7 |
| Phosphorus | → Stable | +0.07 µg/L/yr | 7 |
Reservoir Info (USACE NID)
Mason Lake is a man-made reservoir impounded by the Briggsville (completed 1850), built primarily for recreation on the SOUTH BRANCH NEENAH CREEK; gravity-type dam, 14 ft tall and 250 ft long.
- Surface area
- 856 ac
- Normal storage
- 850 ac-ft
- Max storage
- 700 ac-ft
- Drainage area
- 37 sq mi
- Hazard class
- High
- Owner
- Town of Douglas
Source: USACE National Inventory of Dams, NID ID WI00158 · Operator website
EPA Impairment Status
Mason Lake 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 WI10000764 · Official waterbody report
County Ranking
Ranked #17 of 18 lakes in Adams County
Nearby Lakes With Higher Grades
Mason Lake holds Grade D. 3 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 Adams County
Frequently asked questions about Mason Lake
What is the water quality grade for Mason Lake?
- Mason Lake in Adams County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 1.1 ft visibility. Phosphorus: 105 µg/L. Maximum depth: 9 ft. Surface area: 882 acres.
Is Mason Lake safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Mason Lake has a water quality grade of D (Nutrient-rich). Always check local health department advisories before swimming.
What is the water temperature of Mason Lake?
- Mason Lake typically sits around 76°F at the surface in August, from 20 EPA Water Quality Portal field readings (2024–2026). That is a typical value for the month, not a live reading.
How deep is Mason Lake?
- Mason Lake has a maximum depth of 9 feet. The lake covers 882 acres.
What fish are in Mason Lake?
- Fish species found in Mason Lake include Musky, Panfish, Largemouth Bass, Northern Pike, Catfish. Mason Lake is located in Adams County, Wisconsin.
Are there boat ramps on Mason Lake?
- Mason Lake has 4 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Big Slough, Mason Lake - North, Mason Lake - South, Mason Lake - East. Public access is listed as yes.
Explore Mason Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Wisconsin
Fish species and best lakes in Adams 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
Very high nutrients, dense algae, poor clarity
Wisconsin's cleanest and most-polluted lakes, ranked
More Wisconsin Lake Rankings
State Parks Near Mason Lake
Other Grade D Lakes in Wisconsin
Hypereutrophic Lakes in Wisconsin
Where this data comes from
80 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_WQX80 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
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