Huka Falls is New Zealand's Most Visited Natural Attraction, New Zealand. - stock photo

The Waikato River, New Zealand's longest river, moves gracefully north from Lake Taupo between banks 100 metres apart. Just before the Huka Falls it enters a shallow ravine of hard volcanic rock. The effect is nature's large-scale equivalent of a fire hose feeding into a very fine nozzle. A few hundred metres upstream from the Huka Falls, the Waikato River narrows from approximately 100 metres across into a canyon only 15 metres across.