Saint Mary's River

The St. Marys River, St. Mary's River, or St. Mary River may refer to:

Canada

 * St. Mary River (British Columbia), tributary of the Kootenay River
 * St. Mary's River (Nova Scotia), an important Nova Scotia salmon river

United States

 * St. Marys River (Florida–Georgia), forming a portion of the boundary between Georgia and Florida
 * St. Marys River (Indiana and Ohio), tributary of the Maumee River
 * St. Marys River (Maryland), tributary of the Chesapeake Bay
 * Saint Marys River (Virginia), tributary of the South River

Multi-national

 * St. Mary River (Alberta–Montana), tributary of the Saskatchewan River in Montana and Alberta
 * St. Marys River (Michigan–Ontario), connecting Lake Superior and Lake Huron and forming a portion of the international boundary between the U.S. and Canada