Boulder Lake
Boulder Lake in Oconto County, Wisconsin has a water quality grade of B (Good). Water clarity: 11 ft visibility. Phosphorus: 13.3 µg/L. Maximum depth: 11 ft. Surface area: 370 acres.
Wisconsin DNR lists Panfish as common on Boulder Lake. DNR survey details →
- Clarity
- 11 ft
- Max depth
- 11 ft
- Area
- 370 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Boulder Lake is a 370-acre mesotrophic lake in Oconto County, Wisconsin with a maximum depth of 11 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 5 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Public access is available with 1 public boat landing. Compared to the 38 other monitored lakes in Oconto County, Boulder Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-05-31. Grade methodology: LakeQuality 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 11 ft. Phosphorus level: 13.3 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11 ft | Not graded |
| Phosphorus | 13.3 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Boulder Lake
Compare lakeside cabins, hotels, and vacation rentals near Boulder Lake in Oconto 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 Boulder Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Boulder Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (178,649 cells/mL) on May 16, 2026.
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 Boulder Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Boulder Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 6 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 2003. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Boulder Lake 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).
- 2021Boulder Lake comprehensive summary report, 2021Comprehensive Survey · WI DNR · 2021 (PDF)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 11 ft |
| Surface Area | 370 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Boulder Lake CampgroundPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Public campgrounds near Boulder Lake
- Boulder Lake1.0 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 Boulder 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: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | 0 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.43 µg/L/yr | 6 |
County Ranking
Ranked #1 of 39 lakes in Oconto County
Nearby Lakes in Oconto County
Frequently asked questions about Boulder Lake
Where is Boulder Lake?
- Boulder Lake is a lake in Oconto County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Boulder Lake?
- Boulder Lake in Oconto County, Wisconsin has a water quality grade of B (Good). Water clarity: 11 ft visibility. Phosphorus: 13.3 µg/L. Maximum depth: 11 ft. Surface area: 370 acres.
Is Boulder Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Boulder Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
How deep is Boulder Lake?
- Boulder Lake has a maximum depth of 11 feet. The lake covers 370 acres.
What fish are in Boulder Lake?
- Fish species found in Boulder Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Boulder Lake is located in Oconto County, Wisconsin.
What did the DNR fisheries survey find at Boulder Lake?
- Wisconsin DNR lists Panfish as common on Boulder Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Boulder Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
Does Boulder Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Boulder Lake (clouds, ice, or an off-season gap). The most recent reading was high (178,649 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Are there boat ramps on Boulder Lake?
- Boulder Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Boulder Lake Campground. Public access is listed as yes.
Are there campgrounds on Boulder Lake?
- Boulder Lake has 1 public campground from USGS The National Map within 5 km, including Boulder Lake. 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 Boulder Lake across LakeQuality
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Fish species and best lakes in Oconto County
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its grade
Moderate nutrients, good water quality
Wisconsin's cleanest and most-polluted lakes, ranked
More Wisconsin Lake Rankings
State Parks Near Boulder Lake
Other Grade B Lakes in Wisconsin
Mesotrophic Lakes in Wisconsin
Where this data comes from
46 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_WQX46 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
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