Roubaix Lake
Roubaix Lake is a small lake that is located between Rapid City and Deadwood, South Dakota off Highway 385. There is a small beach, and the lake is great for non-motorized boats and kayaks. They have a large campground that is a little out of the way, so it is nice if you want to get away from the typical crowded areas. There is a fee to use the lake if not camping.
You can walk around the whole lake, but towards the back side of the lake opposite the dam, the trail gets a lot skinnier and more remote. It does take you around the weeds and to the campground on the other side of the lake.