Black Oak Lake vs Boulder Lake
Water quality, depth, fish species, and recreation comparison.
Black Oak Lake and Boulder Lake both received the same overall water quality grade of B (Good). 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 grade differences here are about the lakes themselves, not the agencies grading them. The grades are close: Black Oak Lake (B) and Boulder Lake (B) are within one letter of each other on the LakeGrade rubric. The per-parameter sub-grades below will show where the small differences actually live.
With grades 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 |
|---|---|---|
| Overall Grade | B (Good) | B (Good) |
| Water Clarity | 29 ft | 5.6 ft |
| Phosphorus | 10.6 µg/L | 21.6 µg/L |
| Chlorophyll-a (Algae) | No data | No data |
| Maximum Depth | 85 ft | 23 ft |
| Surface Area | 564 acres | 516 acres |
| Public Access | Yes | Yes |
| Fish Species | 6 | 6 |
| Trophic State | oligotrophic | eutrophic |
Bold value = better for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better).
Verdict
Both lakes earn the same Grade B. 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.
Source: EPA National Aquatic Resource Surveys, 2026.