The Tama River (多摩川, たまがわ, tama-gawa) is a major river in and near Tokyo in Honshu, Japan. Its source is at Mt. Kasadori in Enzan in Yamanashi Prefecture. From there, it flows eastward into Tokyo, where it forms Lake Okutama above the Ogōchi Dam. From there, it takes the name Tama, then flows southward toward Tokyo Bay. Along part of its path, it forms the boundary between Tokyo and Kanagawa Prefecture. Its mouth is at the boundary between Ota-ku in Tokyo and the city of Kawasaki in Kanagawa. The Japanese government classifies it as a first-class river.

During the Edo period, the Tamagawa brothers designed and oversaw the construction of a waterway, the Tamagawa Josui, to divert water from the Tama River at Hamura and carry it to Edo to supply drinking water to the citizens.

Also called

• Ichinose-gawa (Ichinose River) - its upper stream
• Taba-gawa (Taba River) - its upper stream
• Rokugo-gawa (Rokugo River) - near its mouth

Man-made lakes

• Lake Okutama
• Shiromaru Lake