Mary Lake vs Mill Lake
Water quality, depth, fish species, and recreation comparison.
Mary Lake reads lower on nutrients and algae than Mill Lake. Both are in Douglas County, Minnesota.
Both Mary Lake and Mill Lake sit in Minnesota. 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. Mary Lake reads materially cleaner than Mill Lake on nutrients and algae. 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 gap in the readings is decisive: Mary Lake has the lower nutrient and algae numbers. For a researcher, the gap is the interesting part: what is different about the two watersheds, and which of those differences is mutable?
Mary Lake
Good clarity, visible to about 10.5 ft.
Mill Lake
Good clarity, visible to about 11 ft.
Side-by-Side Metrics
| Metric | Mary Lake | Mill Lake |
|---|---|---|
| Water Clarity | 10.5 ft | 11 ft Better |
| Phosphorus | 20 µg/L Better | 23 µg/L |
| Chlorophyll-a (Algae) | 5.5 µg/L Better | 9 µg/L |
| Maximum Depth | 40 ft | 40 ft |
| Surface Area | 2,450 acres | 451 acres |
| Public Access | Yes | Yes |
| Fish Species | 17 Better | 15 |
| Trophic State | mesotrophic | 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
Mary Lake reads lower on nutrients and algae than Mill Lake. Water clarity: 10.5 ft vs 11 ft. For fishing diversity, Mary Lake also leads with 17 species.
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Where to stay near Mary Lake and Mill Lake
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Source: EPA National Aquatic Resource Surveys, 2026.