Ten thousand years ago, as the Ice Age was drawing to a close, Wisconsin's fast-flowing Chippewa River carried vast quantities of sand. Where the Chippewa entered the Mississippi, ten miles downstream from here, its current slowed and the sand settled to the bottom, forming a natural dam that backed up the waters of the Mississippi and created Lake Pepin, one of the most beautiful stretches of the river. Lake Pepin teems with fish, including species whose ancestry can be traced to prehistoric times, among the largest and most unusual of them the sturgeon and the paddlefish. These primitive fish were abundant in Lake Pepin until the 1930s, when the U.S. Army Corps of Engineers began building a network of locks and dams that altered the Mississippi River's flow all the way to St. Louis. Migratory fish such as sturgeon, paddlefish, and skipjack herring could no longer move freely upstream to spawn, and their numbers decreased dramatically. With more than 85 species of fish, Lake Pepin remains a resource for recreational and commercial fishing, including game fish such as northern pike, white bass, black crappie, bluegill, sauger, and walleye, and commercially fished species such as carp, smallmouth buffalo, bigmouth buffalo, flathead catfish, and freshwater drum.