Boulder Lake vs South Turtle Lake
Water quality, depth, fish species, and recreation comparison.
South Turtle Lake reads lower on nutrients and algae than Boulder Lake. Both are in Vilas County, Wisconsin.
Both Boulder Lake and South Turtle 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: Boulder Lake and South Turtle 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.
Boulder Lake
Murky, only visible to about 5.6 ft.
South Turtle Lake
Moderate clarity, visible to about 8 ft.
Side-by-Side Metrics
| Metric | Boulder Lake | South Turtle Lake |
|---|---|---|
| Water Clarity | 5.6 ft | 8 ft Better |
| Phosphorus | 21.6 µg/L | 17.3 µg/L Better |
| Chlorophyll-a (Algae) | No data | No data |
| Maximum Depth | 23 ft | 40 ft Better |
| Surface Area | 516 acres | 466 acres |
| Public Access | Yes | Yes |
| Fish Species | 6 | 6 |
| Trophic State | eutrophic | mesotrophic |
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
Boulder Lake and South Turtle Lake read the same on nutrients and algae overall. The tiebreakers come down to clarity (Boulder Lake: 5.6 ft, South Turtle Lake: 8 ft) and what you want from the lake. Boulder Lake matches its peer on species count.
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Where to stay near Boulder Lake and South Turtle Lake
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Source: EPA National Aquatic Resource Surveys, 2026.