Doubtful Sound is a fjord in Fiordland, in the far south west of New Zealand.

The more famous and more easily accessible Milford Sound is in the same region. But the less accessible Doubtful Sound, sometimes called the ‘Sound of Silence’, offers a powerful serenity. It is the deepest (421 metres) and second longest (40 kilometres) of the South Island’s fiords and is accessed from Manapouri.

Like other fiords in the area, Doubtful Sound contains two distinct layers of water that don’t mix. The top few meters, is fresh water, fed by runoff from the surrounding mountains. Below this is a layer of salt water from the sea.

The difference in refractive index between these two layers makes it difficult for light to penetrate. As a result, many deep-sea species — such as black coral — grow in the comparatively shallow depths in Fiordland’s sounds.

Doubtful Sound has some splendid waterfalls, particularly during the wetter seasons. In the Hall Arm, the Browne Falls cascades 619 metres; Helena Falls at Deep Cove tumbles 220 metres.

Wildlife is another reason to visit this fiord. Keep an eye out for bottlenose dolphins, fur seals and penguins.