Boulder Lake
Boulder Lake in Vilas County, Wisconsin has a water quality grade of B (Good). Water clarity: 5.6 ft visibility. Phosphorus: 21.6 µg/L. Maximum depth: 23 ft. Surface area: 516 acres.
Wisconsin DNR rates Walleye as abundant on Boulder Lake. DNR survey details →
- Clarity
- 5.6 ft
- Max depth
- 23 ft
- Area
- 516 acres
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Vilas County
Swipe left or right on this bar to open the next or previous lake.
Boulder Lake is a 516-acre productive, nutrient-rich eutrophic lake in Vilas County, Wisconsin with a maximum depth of 23 feet. Water quality is graded B based on 1 sampling years through 2021. Overall water quality is improving over recent sampling years. The lake supports 6 documented fish species including Musky, Panfish, and Largemouth Bass. Public access is available with 2 public boat landings. Compared to the 102 other monitored lakes in Vilas County, Boulder Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2021-08-17. Grade methodology: LakeGrade methodology.
Watch Boulder Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Grade onlyLimited data
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)
Murky, only visible to about 5.6 ft. Phosphorus level: 21.6 µg/L. Trophic State Index: 50.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.6 ft | Not graded |
| Phosphorus | 21.6 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 50 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Boulder Lake
Compare lakeside cabins, hotels, and vacation rentals near Boulder 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 Boulder Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
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 moderate (75,858 cells/mL) on May 30, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR rates Walleye as abundant 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 2 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. 1 station on file (most recent sample 2021).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 23 ft |
| Surface Area | 516 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Boulder LakePublic
- Boulder LakePublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
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 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.25 m/yr | 2 |
County Ranking
Ranked #1 of 103 lakes in Vilas County
Nearby Lakes in Vilas County
Frequently asked questions about Boulder Lake
Where is Boulder Lake?
- Boulder Lake is a lake in Vilas 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 Vilas County, Wisconsin has a water quality grade of B (Good). Water clarity: 5.6 ft visibility. Phosphorus: 21.6 µg/L. Maximum depth: 23 ft. Surface area: 516 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 23 feet. The lake covers 516 acres.
What fish are in Boulder Lake?
- Fish species found in Boulder Lake include Musky, Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Boulder Lake is located in Vilas County, Wisconsin.
What did the DNR fisheries survey find at Boulder Lake?
- Wisconsin DNR rates Walleye as abundant 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 2 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 moderate (75,858 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 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Boulder Lake, Boulder Lake. Public access is listed as yes.
Explore Boulder 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 Vilas County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Northwoods Wisconsin area
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
Other Grade B Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Compare Boulder Lake With Nearby Lakes
Vilas County · Grade C
Vilas County · Grade B
Vilas County · Grade B
Vilas County · Grade B
Vilas County · Grade B
Vilas County · Grade B
Where this data comes from
7 measurements from 1 monitoring station, 2020–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX7 samples · 2020–2021
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