Milford Sound / Piopiotahi is one of roughly 90 places to have been given a dual name as part of a 1998 Treaty of Waitangi settlement with Ngāi Tahu, recognising the significance of the fiord to both Māori and Pākehā New Zealanders.

[13] After heavy rain temporary waterfalls can be seen running down the steep sided rock faces that line the fiord.

[14] The rainfall creates dozens of temporary waterfalls (as well as several major, more permanent ones) cascading down the cliff faces, some reaching a thousand metres in length.

Accumulated rainwater can, at times, cause portions of the rain forest to lose their grip on the sheer cliff faces, resulting in tree avalanches into the fiord.

Milford Sound is home to a variety of marine mammals, including seals and the southernmost wild population of bottlenose dolphins.

[22] This filters much of the sunlight which enters the water, allowing for a variety of Black coral to be found at depths of as shallow as 10 metres (33 ft), significantly closer to the surface than usual.

[23] Milford Sound was initially overlooked by European explorers because its narrow entry did not appear to lead into such large interior bays.

Sailing ship captains such as James Cook, who bypassed Milford Sound on his journeys for just this reason, also feared venturing too close to the steep mountainsides, afraid that wind conditions would prevent escape.

The fiord remained undiscovered by Europeans until Captain John Grono discovered it c. 1812 and named it Milford Haven after his homeland in Wales.

[26] Following the passage of the Ngāi Tahu Claims Settlement Act 1998, the name of the fiord was officially altered to Milford Sound / Piopiotahi.

[29][30] This makes the sound one of New Zealand's most-visited tourist spots even with its remote location and long journey times from the nearest population centres.

The long distance to the sound means that tourist operators from Queenstown all depart very early in the day, arriving back only late in the evening.

A hose was apparently used to displace the fuel from the tanks of one of the tour vessels, and various government officials claimed it appeared to be an act of ecoterrorism motivated by rising numbers of tourists to the park,[35] though more details did not become known.