is in Tokyo and Yamanashi Prefectures in Japan. Lying above the Ogà Âchi Dam, it is also known as the Ogà Âchi Reservoir. Lake Okutama is an important source of drinking water for Tokyo.
The lake occupies part of the town of Okutama in Nishitama District, Tokyo and the village of Tabayama in Kitatsuru District, Yamanashi.
The Taba (Tama) River feeds Lake Okutama at its western end. From the southwest, the Kosuge River also flows into the lake. The Tama River drains the lake at the eastern end. The surroundings are famous for cherry blossoms in the spring.