Mann Lake
Mann Lake in Vilas County, Wisconsin has a water quality grade of C (Fair). Water clarity: 6.8 ft visibility. Phosphorus: 32.9 µg/L. Maximum depth: 18 ft. Surface area: 253 acres.
Wisconsin DNR lists Panfish as common on Mann Lake. DNR survey details →
- Clarity
- 6.8 ft
- Typical in August
- 76°F
- Max depth
- 18 ft
- Area
- 253 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
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Mann Lake is a 253-acre productive, nutrient-rich eutrophic lake in Vilas County, Wisconsin with a maximum depth of 18 feet. Water quality is graded C based on 1 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 2 documented fish species including Panfish and Northern Pike. Public access is available with 1 public boat landing. Compared to the 102 other monitored lakes in Vilas County, Mann Lake ranks #91 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-08-23. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Moderate clarity, visible to about 6.8 ft. Phosphorus level: 32.9 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.8 ft | Not graded |
| Phosphorus | 32.9 µg/L | Fair |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Mann Lake
Compare lakeside cabins, hotels, and vacation rentals near Mann Lake in Vilas 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 Mann Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Mann Lake typically sits around 76°F at the surface in August. Summer average is about 73°F. Usually warmest in Jul (about 76°F) and coldest in Apr (about 46°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 14 field readings (2024–2025) via the EPA Water Quality Portal. See the full Mann Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Mann Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (409,261 cells/mL) on November 15, 2025.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR lists Panfish as common on Mann Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Mann Lake C from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is declining. 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 1995. 9 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 18 ft |
| Surface Area | 253 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Mann LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Mann 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.
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.446 m/yr | 6 |
| Phosphorus | → Stable | +0.27 µg/L/yr | 6 |
County Ranking
Ranked #91 of 103 lakes in Vilas County
Nearby Lakes With Higher Grades
Mann Lake holds Grade C. 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 Vilas County
Frequently asked questions about Mann Lake
Where is Mann Lake?
- Mann Lake is a lake in Vilas County, Wisconsin. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Mann Lake?
- Mann Lake in Vilas County, Wisconsin has a water quality grade of C (Fair). Water clarity: 6.8 ft visibility. Phosphorus: 32.9 µg/L. Maximum depth: 18 ft. Surface area: 253 acres.
Is Mann Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Mann Lake has a water quality grade of C (Fair). Always check local health department advisories before swimming.
What is the water temperature of Mann Lake?
- Mann Lake typically sits around 76°F at the surface in August, from 14 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Mann Lake?
- Mann Lake has a maximum depth of 18 feet. The lake covers 253 acres.
What fish are in Mann Lake?
- Fish species found in Mann Lake include Panfish, Northern Pike. Mann Lake is located in Vilas County, Wisconsin.
What did the DNR fisheries survey find at Mann Lake?
- Wisconsin DNR lists Panfish as common on Mann Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Mann Lake C from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Does Mann Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Mann Lake (clouds, ice, or an off-season gap). The most recent reading was high (409,261 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Are there boat ramps on Mann Lake?
- Mann Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Mann Lake. Public access is listed as yes.
Explore Mann Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
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Fish species and best lakes in Vilas County
Species activity outlook by water temperature and season
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Where to stay at Wisconsin's top lakes, each with its grade
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High nutrients, frequent algae, reduced clarity
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Other Grade C Lakes in Wisconsin
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Where this data comes from
45 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX45 samples · 2020–2025
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
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