Mary River is a waterway in the U.S. state of Alaska. Situated on the northwestern portion of Seward Peninsula, it was included in the Agiapuk River mining district. The Mary River has a length of about 20 miles (32 km) and flows into the upper end of Imuruk Basin. About 5 miles (8.0 km) from its mouth, the river forks, the two branches being of about equal size. The lower part of the course of the Mary River is within the flats which border Imuruk Basin. Above these flats, the valleys of the two branches of the Mary River are wide, and within them, the rivers meander over broad flood plains. Between the forks of the river there is a broad, flat-topped ridge, with an elevation of 700 feet (210 m), which is partly covered with washed gravel. At the edge of the Imuruk lowlands, where the Mar