More than 11 square miles of marshes, savannas, oak forests, and other landscapes drain into Lake Michigan through the Dunes Creek watershed, which encompasses all of Indiana Dunes State Park. The park's nature preserve is designated as a National Natural Landmark and is one of the best remaining examples of undeveloped and relatively unspoiled dune landscape along the southern shore of Lake Michigan. More rare, threatened, and endangered plants and animals inhabit the park than nearly anywhere else in the Midwest. A watershed is an area of land that drains to a common waterway, and water draining from surrounding land can carry contaminants that pollute the water. Watershed management offers a way to cross traditional boundaries and bring people in a region together to make responsible land use choices. To protect water quality, Save the Dunes worked with stakeholders and communities to develop a watershed management plan funded and approved by the Indiana Department of Environmental Management, identifying water quality concerns within the watershed and strategies to address them. Today, Indiana Dunes State Park is working with Save the Dunes to implement those strategies and protect water quality. Dunes Creek's rusty brown color comes from tannins, naturally occurring pigments in many plants, especially oak trees, whose bark, leaves, and acorns contain tannins that help defend against insects and fungal attacks; when leaves and nuts fall to the ground within the watershed, rainwater washes the tannins into Dunes Creek, giving it a rusty orange-brown color.