Okutama Rafting - White water Rafting in the Tama River at Okutama. Flowing from its source in the mountains in Yamanashi, the Tama River makes its way to the ocean after traversing a nearly 140 kilometer long path. The river is dammed along the way, forming Lake Okutama, a major source of Tokyo's drinking water. Many people enjoy a variety of water sports on the river. The Tama River provides the perfect location for packrafting. with over eight kilometers of rapids with crystal clear water that wind through native bush. There is plenty of wildlife to spot as you cruise down sections of unspoiled greenery - hard to believe you are within the city limits of Tokyo!