However the Tongariro Power Scheme utilised Rotoaira as a storage lake for the Tokaanu Hydropower Station. Extensive engineering works were carried out including the diversion of a number of other streams (including Whanganui River) into Rotoaira via the Otamangakau Hydro Lake and construction of a tunnel through Pihanga to the Tokaanu Power Station. Damming of the Poutu outlet has created Motuopuhi island, formerly a peninsula.