Beginning in Upper St. Croix Lake in Douglas County, Wisconsin, the St. Croix River flows 164 miles to its confluence with the Mississippi River near Prescott, Wisconsin. The majority of the river creates the state boundary between Minnesota and Wisconsin. The upper St. Croix River flows past heavily wooded banks and islands. The upper 200 miles of the river is federally designated as a Wild and Scenic River. The lower St. Croix River showcases steep sandstone and limestone bluffs with winding side channels. This segment is also federally designated as a wild and scenic river.
Trees play a vital role in protecting and supporting riverbank ecosystems. Their roots stabilize soil and reduce erosion, helping keep riverbanks intact during heavy rain and flooding. Leaves and organic matter from trees also add nutrients like nitrogen to the water and surrounding soil, which support algae and aquatic plants.
Trees act as natural filters. Their roots and surrounding soil absorb nutrients like nitrogen and phosphorus from runoff before they reach the river, reducing pollution and helping maintain healthier water for fish and wildlife.
Fallen leaves and organic matter provide nutrients that support aquatic insects and plants, which form the base of the food chain for fish. Overhanging branches also create shade and shelter for fish, birds, and other animals.
