Lake Okutama (奥多摩湖, Okutama-ko) is in Tokyo and Yamanashi Prefectures in Japan.

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.

The Tama River drains the lake at the eastern end.