Miyajima-numa is located about 45 kilometers northeast of Sapporo, on the western edge of Bibai City. The Ishikari River flows on the west side of the swamp, and the mountains of Sakhalin stand on the other side of the river. The swamp is surrounded by a vast countryside.
In November 2002, Miyajima-numa was registered under the Ramsar Convention as a "wetland of international importance. There are 12 Ramsar sites in Hokkaido, including Lake Utonai and Kushiro Marsh (33 sites in Japan). The Ramsar Convention is an international treaty to protect wetlands and the creatures that live there.