Byllesby Lake vs Marion Lake
Water quality, depth, fish species, and recreation comparison.
Marion Lake has a higher water quality grade (A, Excellent) than Byllesby Lake (F, Very Poor). Both are in Dakota County, Minnesota.
Both Byllesby Lake and Marion 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. Marion Lake (A) is materially cleaner than Byllesby Lake (F). A gap that wide is unlikely to close in a single year of remediation work; it reflects multi-decade differences in the lakes themselves.
For a recreational visitor, the wider grade gap is decisive — Marion 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?
Byllesby Lake
Very murky, less than 3 ft of visibility.
Marion Lake
Moderate clarity, visible to about 7 ft.
Side-by-Side Metrics
| Metric | Byllesby Lake | Marion Lake |
|---|---|---|
| Overall Grade | F (Very Poor) | A (Excellent) |
| Water Clarity | 3 ft | 7 ft |
| Phosphorus | 227 µg/L | 20 µg/L |
| Chlorophyll-a (Algae) | 40.7 µg/L | 4.6 µg/L |
| Maximum Depth | 50 ft | 21 ft |
| Surface Area | 1,368 acres | 530 acres |
| Public Access | Yes | Yes |
| Fish Species | 19 | 14 |
| Trophic State | hypereutrophic | mesotrophic |
Bold value = better for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better).
Verdict
Marion Lake wins on overall water quality with a Grade A versus Byllesby Lake's Grade F. Water clarity: 7 ft vs 3 ft. For more fish-species variety, Byllesby Lake edges ahead with 19 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.