Big Portage Lake vs Boulder Lake
Water quality, depth, fish species, and recreation comparison.
Big Portage Lake and Boulder Lake both received the same overall water quality grade of B (Good). Both are in Vilas County, Wisconsin.
Big Portage Lake and Boulder Lake are both in Wisconsin — a same-state head-to-head where the comparison comes down to lake-specific differences in depth, watershed, and monitoring history rather than the broader state-level water-quality regime. The grades are close: Big Portage 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.
Big Portage Lake
Crystal clear, you can see 18.5 ft down.
Boulder Lake
Murky, only visible to about 5.6 ft.
Side-by-Side Metrics
| Metric | Big Portage Lake | Boulder Lake |
|---|---|---|
| Overall Grade | B (Good) | B (Good) |
| Water Clarity | 18.5 ft | 5.6 ft |
| Phosphorus | 12 µg/L | 21.6 µg/L |
| Chlorophyll-a (Algae) | No data | No data |
| Maximum Depth | 40 ft | 23 ft |
| Surface Area | 586 acres | 516 acres |
| Public Access | Yes | Yes |
| Fish Species | 4 | 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 (Big Portage Lake: 18.5 ft, Boulder Lake: 5.6 ft) and what you want from the lake. Big Portage Lake has fewer fish species than Boulder Lake.
Source: EPA National Aquatic Resource Surveys, 2026.