Ann Lake vs Knife Lake
Water quality, depth, fish species, and recreation comparison.
Ann Lake and Knife Lake both received the same overall water quality grade of F (Algae-prone). Both are in Kanabec County, Minnesota.
Ann Lake and Knife Lake are both in Minnesota — a same-state head-to-head where the comparison comes down to lake-specific differences in depth, watershed, and monitoring history rather than the broader state-level water-quality regime. These two are within a letter of each other on the rubric — Ann Lake (F) versus Knife Lake (F). The deciding factors for a recreational visitor are likely physical (depth, access, fish species) rather than water-quality differences.
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.
Ann Lake
Very murky, less than 2 ft of visibility.
Knife Lake
Very murky, less than 2 ft of visibility.
Side-by-Side Metrics
| Metric | Ann Lake | Knife Lake |
|---|---|---|
| Overall Grade | F (Algae-prone) | F (Algae-prone) |
| Water Clarity | 2 ft | 2 ft |
| Phosphorus | 73.5 µg/L Better | 161.5 µg/L |
| Chlorophyll-a (Algae) | 57 µg/L Better | 97.2 µg/L |
| Maximum Depth | 17 ft Better | 15 ft |
| Surface Area | 653 acres | 1,259 acres |
| Public Access | Yes | Yes |
| Fish Species | 13 | 19 Better |
| Trophic State | eutrophic | hypereutrophic |
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.
Verdict
Both lakes earn the same Grade F. The tiebreakers come down to clarity (Ann Lake: 2 ft, Knife Lake: 2 ft) and what you want from the lake. Ann Lake has fewer fish species than Knife Lake.
Source: EPA National Aquatic Resource Surveys, 2026.