The Au Gres River is a river in Michigan. Its mouth is at Lake Huron in the city of Au Gres, Michigan. It flows through Arenac, Iosco and Ogemaw counties. It formerly had an eastern branch, which was severed from the parent river and rerouted along the Whitney Drain to Lake Huron north of Au Gres. The main stream is 46.7 miles (75.2 km) long.