Portage Lake vs Six Mile Lake
Water quality, depth, fish species, and recreation comparison.
Six Mile Lake has a higher water quality grade (A, Excellent) than Portage Lake (C, Fair). Both are in Cass County, Minnesota.
Both Portage Lake and Six Mile Lake sit in Minnesota. 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 meaningfully apart: Six Mile Lake grades a A while Portage Lake grades a C. That two-letter spread reflects real underlying differences — different watershed inputs, different depth profiles, or different monitoring rigor.
For a recreational visitor, the wider grade gap is decisive — Six Mile Lake is the better water-quality choice. For a researcher, the gap is the interesting part: what is different about the two watersheds, and which of those differences is mutable?
Portage Lake
Moderate clarity, visible to about 7.5 ft.
Six Mile Lake
Good clarity, visible to about 11.5 ft.
Side-by-Side Metrics
| Metric | Portage Lake | Six Mile Lake |
|---|---|---|
| Overall Grade | C (Fair) | A (Excellent) |
| Water Clarity | 7.5 ft | 11.5 ft |
| Phosphorus | 22 µg/L | 14.5 µg/L |
| Chlorophyll-a (Algae) | 7.1 µg/L | 6.7 µg/L |
| Maximum Depth | 55 ft | 68 ft |
| Surface Area | 1,539 acres | 1,323 acres |
| Public Access | Yes | Yes |
| Fish Species | 15 | 16 |
| Trophic State | mesotrophic | mesotrophic |
Bold value = better for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better).
Verdict
Six Mile Lake wins on overall water quality with a Grade A versus Portage Lake's Grade C. Water clarity: 11.5 ft vs 7.5 ft. For fishing diversity, Six Mile Lake also leads with 16 species.
Source: EPA National Aquatic Resource Surveys, 2026.