Five rivers—the Kiamichi, Ouachita, Cossatot, Poteau, and Little Missouri—originate in Polk County. The Cossatot begins in the Ouachita Mountains southeast of Mena and flows south for about 26 miles to Gillham Lake. The Cossatot is considered to be the toughest river in Arkansas to navigate and is famous for its Class IV and V rapids. The word "Cossatot" is an Indian word meaning "skull-crusher."
Cossatot River State Park-Natural Area is Arkansas' 48th state park. The park is located between Ark. 246 and U.S. 278 near Wickes. It is the largest natural area in the state and conserves a twelve-and-one-half-mile stretch of the Cossatot River. The park/natural area is also home to two types of fish—the Ouachita Mountain shiner and the leopard darter—that are found only in streams of the Ouachita Mountains. Several rare plant species are found within the park/natural area's five major plant communities.