Gennojo Oba was a river conservation expert. Headman of the Fukura Village in Suruga Province ( Shizuoka Prefecture).
Gennojo Oba was born in 1660.
Because farmers in 28 villages in his native district were suffering from shortage of water for rice fields, Gennojo Oba undertook to draw the water of Lake Ashi in Hakone to the area (1662). Commissioned Yoemon Tomono, a civil engineer in Edo, to excavate a 1,500-meter tunnel under Mt. Hakone to bring water from the lake. It was started in 1666 and completed in two years. A total of 830,000 men were employed in the work. The tunnel has irrigated a total of 1,300 acres of rice fields.