The Tama River is a Class A river with a total length of 138km and a basin area of 1,240km², originating from Mount Kasatori in Yamanashi Prefecture and flowing along the border of Tokyo and Kanagawa into Tokyo Bay.

Despite a history of pollution and flooding (such as the 1974 Komae flood), the water quality has since improved, allowing sweetfish to return, and the riverbanks have become a beloved recreational space for the public.