Sylvan Lake vs Thunder Lake
Water quality, depth, fish species, and recreation comparison.
Sylvan Lake and Thunder Lake both received the same overall water quality grade of A (Excellent). Both are in Cass County, Minnesota.
Both Sylvan Lake and Thunder 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. These two are within a letter of each other on the rubric — Sylvan Lake (A) versus Thunder Lake (A). 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.
Sylvan Lake
Crystal clear, you can see 19.8 ft down.
Thunder Lake
Crystal clear, you can see 16.4 ft down.
Side-by-Side Metrics
| Metric | Sylvan Lake | Thunder Lake |
|---|---|---|
| Overall Grade | A (Excellent) | A (Excellent) |
| Water Clarity | 19.8 ft | 16.4 ft |
| Phosphorus | 7 µg/L | 10 µg/L |
| Chlorophyll-a (Algae) | No data | No data |
| Maximum Depth | - | - |
| Surface Area | 1.3K acres | 1.3K acres |
| Public Access | Unknown | Unknown |
| Fish Species | 0 | 1 |
| Trophic State | oligotrophic | oligotrophic |
Bold value = better for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better).
Verdict
Both lakes earn the same Grade A. The tiebreakers come down to clarity (Sylvan Lake: 19.8 ft, Thunder Lake: 16.4 ft) and what you want from the lake. Sylvan Lake has fewer fish species than Thunder Lake.