It runs for 425 kilometres from the eastern slopes of Mount Ruapehu , joining the Tongariro River system and emptying into Lake Taupo , New Zealand 's largest lake .
The Waikato River is the longest river in New Zealand .
Waikato River runs for 425 kilometres from the eastern slopes of Mount Ruapehu , joining the Tongariro River system and emptying into Lake Taupo , New Zealand 's largest lake .
The Waikato River is the longest river in New Zealand .