Big Carnelian Lake

Big Carnelian Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Washington County. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. The lake's 66 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. The lake's 457 acres and 5.1 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Among the 83 graded lakes in Washington County, Big Carnelian Lake ranks 2 — in the top quartile locally.

Big Carnelian Lake is on the Minnesota infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. The fishery includes walleye alongside the lake's other 12 documented species — a notable draw for Minnesota anglers. A documented public access point at Big Carnelian Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The lake has a partial ice record — 23 observed ice-outs, centered near Apr 9. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.