 Its mountainous upper reaches and tributaries were areas of steep valleys and abundant rainfall, and were sparsely populated.However, the bulk of investment in hydroelectric power generation in the region was centered on the Ōi River, and it was not until the Taishō period that development began on the Tenryū River.Private entrepreneur Fukuzawa Momosuke founded the , which later became before it was nationalized into the pre-war government monopoly in 1938.