Doubtful Sound / Patea is a fjord in Fiordland, in the far south west of New Zealand. It is located in the same region as the smaller but more famous and accessible Milford Sound. It took second place after Milford Sound as New Zealand's most famous tourism destination.
At 40 kilometres (25 mi) long, Doubtful Sound is the second longest, and with a depth of up to 421 metres (1,381 ft) the deepest of the South Island's fiords. In comparison with Milford Sound, it is more widespread, with the cliffs not as dramatically tall and near vertical.
Doubtful Sound was named 'Doubtful Harbour' in 1770 by Captain Cook, who did not enter the inlet as he was uncertain whether it was navigable under sail. It was later renamed Doubtful Sound by whalers and sealers, although it is not technically a sound but a fiord.