Castle Rock Lake Started in 1947 and finished in 1951 by the Wisconsin River Power Company, Castle Rock Lake is Wisconsin's fourth largest lake. It covers sixteen thousand acres, has approximately sixty miles of shoreline and is ideal for fishing, boating, water-skiing and tubing. The lake's depth varies from 8 to 20 feet in most places, with area in the old river beds reaching as deep as 30 feet. The structure created from the river beds makes Castle Rock a very productive and consistent fishing lake. While walleyes, white bass, and crappies are the most abundant, many northern pike, large mouth bass, small mouth bass and pan-fish are taken also.