Lake Koshkonong vs Rock Lake
Water quality, depth, fish species, and recreation comparison.
Rock Lake reads lower on nutrients and algae than Lake Koshkonong. Both are in Jefferson County, Wisconsin.
Both Lake Koshkonong and Rock Lake sit in Wisconsin. 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. Rock Lake reads materially cleaner than Lake Koshkonong 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: Rock 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?
Lake Koshkonong
Very murky, less than 1.7 ft of visibility.
Rock Lake
Good clarity, visible to about 12 ft.
Side-by-Side Metrics
| Metric | Lake Koshkonong | Rock Lake |
|---|---|---|
| Water Clarity | 1.7 ft | 12 ft Better |
| Phosphorus | 287 µg/L | 18.1 µg/L Better |
| Chlorophyll-a (Algae) | No data | No data |
| Maximum Depth | 7 ft | 60 ft Better |
| Surface Area | 10,595 acres | 1,365 acres |
| Public Access | Yes | Yes |
| Fish Species | 7 Better | 5 |
| Trophic State | hypereutrophic | 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.
Swap a lake
Compare Lake Koshkonong or Rock Lake against a different lake.
Verdict
Rock Lake reads lower on nutrients and algae than Lake Koshkonong. Water clarity: 12 ft vs 1.7 ft. For more fish-species variety, Lake Koshkonong edges ahead with 7 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.