Deep Cove is an arm of Doubtful Sound, a deep indentation in the southwest coast of New Zealand's South Island. Along with the Hall Arm, which lies to the southwest of Deep Cove, it forms one of the two most remote parts of the sound from the Tasman Sea, with its mouth being 32 kilometres (20 mi) from the mouth of Doubtful Sound. Elizabeth Island lies close to the junction of Deep Cove and the Hall Arm. The cove is home to several notable waterfalls, notably Helena Falls and Lady Alice Falls.
Until the 1960s, Deep Cove was only accessible from the sea or via the Wilmot Pass walking track. In 1964, however, the cove saw the start of considerable activity as it became an important part of the Manapouri Hydroelectricity Project as the site of the tailrace tunnel from Lake Manapouri. A 10 kilometres (6.2 mi) tunnel connects the cove with the lake. The tunnel was completed in late 1969, with the power station became operational the following year. A second tunnel was started in 1997 and became operational in 2002.