This graph shows the top 10 rivers in New Zealand, based on the average amount of water they would discharge into the sea every second if their natural flow was not diverted for hydroelectric power or irrigation. Eight are in the South Island and have catchments extending into the Southern Alps. Most of the Waiau River’s water is now diverted to Doubtful Sound through the Manapouri power station, and significant volumes of Rakaia River water are applied to irrigation. In the North Island, some of the headwater streams of the Whanganui and Rangitīkei rivers have been diverted into the Waikato River.