Mercer Lake
Mercer Lake in Iron County, Wisconsin has a water quality grade of B (Good). Water clarity: 12 ft visibility. Phosphorus: 15.7 µg/L. Maximum depth: 24 ft. Surface area: 181 acres.
- Clarity
- 12 ft
- Max depth
- 24 ft
- Area
- 181 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Iron County
Mercer Lake is a 181-acre mesotrophic lake in Iron County, Wisconsin with a maximum depth of 24 feet. Water quality is graded B based on 1 sampling years through 2026. Overall water quality is improving over recent sampling years. The lake supports 7 documented fish species including Musky, Panfish, and Largemouth Bass. Public access is available with 1 public boat landing. Compared to the 15 other monitored lakes in Iron County, Mercer Lake ranks #14 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-28. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
Good clarity, visible to about 12 ft. Phosphorus level: 15.7 µg/L. Trophic State Index: 43.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 12 ft | Not graded |
| Phosphorus | 15.7 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Mercer Lake
Compare lakeside cabins, hotels, and vacation rentals near Mercer Lake in Iron 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.
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Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 24 ft |
| Surface Area | 181 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Mercer LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Mercer 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 2001. 5 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 | → Stable | -0.05 m/yr | 6 |
| Phosphorus | ↑ Improving | -1.12 µg/L/yr | 7 |
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Mercer Lake under Clean Water Act (NPDES) discharge permits.
- Mercer Sanitary District No 1Mercer · 1 mi away · NPDES WI0029602
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 #14 of 16 lakes in Iron County
Nearby Lakes in Iron County
Frequently asked questions about Mercer Lake
What is the water quality grade for Mercer Lake?
- Mercer Lake in Iron County, Wisconsin has a water quality grade of B (Good). Water clarity: 12 ft visibility. Phosphorus: 15.7 µg/L. Maximum depth: 24 ft. Surface area: 181 acres.
Is Mercer Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Mercer Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
How deep is Mercer Lake?
- Mercer Lake has a maximum depth of 24 feet. The lake covers 181 acres.
What fish are in Mercer Lake?
- Fish species found in Mercer Lake include Musky, Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye, Sturgeon. Mercer Lake is located in Iron County, Wisconsin.
Are there boat ramps on Mercer Lake?
- Mercer Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Mercer Lake. Public access is listed as yes.
Explore Mercer Lake across LakeGrade
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Where this data comes from
29 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_WQX29 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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
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