The Mowich River is a river in the U.S. state of Washington. Its watershed drains a portion of the western side of Mount Rainier, part of the Cascade Range. The river has two main headwater branches, the South Mowich River and the North Mowich River. The South Mowich is significantly larger and sometimes considered the main river. The Mowich and its tributaries drain several of Mount Rainier's glaciers. The upper portion of its watershed is contained within Mount Rainier National Park.