New Zealand - Waikato River - The Waikato River at Taupo. - 1910 - 1920 Period - Real Photo Postcard Format #334680 - The Waikato River is the longest river in New Zealand, running for 425 kilometres (264 mi) through the North Island. - The present course of the river was largely formed about 17,000 years ago. - The name Waikato comes from the Māori language and translates as flowing water.