Black Oak Lake vs Boulder Lake
Water quality, depth, fish species, and recreation comparison.
Black Oak Lake reads lower on nutrients and algae than Boulder Lake. Both are in Vilas County, Wisconsin.
Both Black Oak Lake and Boulder Lake sit in Wisconsin. A same-state comparison strips out the state-level water-quality regime as a variable: any differences in the readings here are about the lakes themselves, not the agencies sampling them. The readings are close: Black Oak Lake and Boulder Lake sit within a narrow band of each other on phosphorus, chlorophyll-a and clarity. The per-parameter table below shows where the small differences actually live.
With readings this close, the choice between the two lakes turns on non-water-quality factors: depth, fish species, public access, distance from home. The per-lake pages below cover all of those.
Black Oak Lake
Crystal clear, you can see 29 ft down.
Boulder Lake
Murky, only visible to about 5.6 ft.
Side-by-Side Metrics
| Metric | Black Oak Lake | Boulder Lake |
|---|---|---|
| Water Clarity | 29 ft Better | 5.6 ft |
| Phosphorus | 10.6 µg/L Better | 21.6 µg/L |
| Chlorophyll-a (Algae) | No data | No data |
| Maximum Depth | 85 ft Better | 23 ft |
| Surface Area | 564 acres | 516 acres |
| Public Access | Yes | Yes |
| Fish Species | 6 | 6 |
| Trophic State | oligotrophic | eutrophic |
A green ✓ marks the better value for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better). Surface area and trophic state carry no tick — a bigger lake is not a better lake.
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Verdict
Black Oak Lake and Boulder Lake read the same on nutrients and algae overall. The tiebreakers come down to clarity (Black Oak Lake: 29 ft, Boulder Lake: 5.6 ft) and what you want from the lake. Black Oak Lake matches its peer on species count.
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Where to stay near Black Oak Lake and Boulder Lake
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Source: EPA National Aquatic Resource Surveys, 2026.