Lake Okutama (奥多摩湖, Okutama-ko) is in Tokyo and Yamanashi Prefectures in Japan. Lying above the Ogōchi Dam, it is also known as the Ogōchi 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.

• Dam height: 148 m
• Dam length: 353 m
• Greatest depth: 142 m
• Mean depth: 43.6 m
• Circumference when full: 45.37 km
• Altitude of surface when full: 526.5 m
• Area of surface when full: 4.25 km²
• Capacity: 185,400,000 m³
• Completion: 1957
• Displaced: 945 households
• Died during construction: 87 people

• Tokyo Metropolitan Government Bureau of Waterworks
• Japan National Tourism Organization
• Go Tokyo, Official Tokyo Travel Guide