Strait, separating North and South islands of New Zealand. Extending from the Tasman Sea to the Pacific Ocean, it is about 14 mi (23 km) wide at its narrowest point and averages 420 ft (128 m) in depth. Both shores are lined with steep cliffs, and that of South Island is deeply embayed. Treacherous currents and fierce storms present serious hazards to navigation. Capt. James Cook explored the strait in 1770.