Ash Lake vs Blackduck Lake
Water quality, depth, fish species, and recreation comparison.
Ash Lake has a higher water quality grade (C, Fair) than Blackduck Lake (D, Nutrient-rich). Both are in St. Louis County, Minnesota.
Both Ash Lake and Blackduck 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 close: Ash Lake (C) and Blackduck Lake (D) 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.
Ash Lake
Murky, only visible to about 5.5 ft.
Blackduck Lake
Moderate clarity, visible to about 6.8 ft.
Side-by-Side Metrics
| Metric | Ash Lake | Blackduck Lake |
|---|---|---|
| Overall Grade | C (Fair) Better | D (Nutrient-rich) |
| Water Clarity | 5.5 ft | 6.8 ft Better |
| Phosphorus | 39 µg/L Better | 43 µg/L |
| Chlorophyll-a (Algae) | 11.1 µg/L Better | 23.3 µg/L |
| Maximum Depth | 25 ft | 30 ft Better |
| Surface Area | 690 acres | 1,250 acres |
| Public Access | Yes | Yes |
| Fish Species | 9 Better | 8 |
| Trophic State | eutrophic | eutrophic |
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.
Swap a lake
Compare Ash Lake or Blackduck Lake against a different lake.
Verdict
Ash Lake wins on overall water quality with a Grade C versus Blackduck Lake's Grade D. Water clarity: 5.5 ft vs 6.8 ft. For fishing diversity, Ash Lake also leads with 9 species.
Source: EPA National Aquatic Resource Surveys, 2026.