The Causeway Street Marshes are a wetland complex located in Medfield. They are part of the Charles River watershed and provide habitats for a variety of wildlife. The marshes are a valuable natural resource for flood control, water quality improvement, recreation, and education. The marshes are managed by the Massachusetts Department of Conservation and Recreation (DCR) and are open to the public for passive enjoyment.

Causeway Street traverses marshes parallel to Sewall Brook and the bridge crossing the Stop River.