They are fed by rain water drenched moss and will last a few days at most once the rain stops. Climate With a mean annual rainfall of each year, a high level even for the West Coast, Milford Sound is known as the wettest inhabited place in New Zealand and one of the wettest in the world. Rainfall can reach during a span of 24 hours. The rainfall creates dozens of temporary waterfalls (as well as a number of major, more permanent ones) cascading down the cliff faces, some reaching a thousand metres in length. Smaller falls from such heights may never reach the bottom of the sound, drifting away in the wind. 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. The regrowth of the rain forest after these avalanches can be seen in several locations along the sound. Wildlife Milford Sound is home to a variety of marine mammals, including seals and the southernmost wild population of bottlenose dolphins. Whales, especially the humpback and southern right whales, are increasingly observed due to recoveries of each species. Penguins are also common within the sound, which is a breeding site for the Fiordland penguin and has subsequently been identified as an Important Bird Area by BirdLife International. As a result of Milford Sound's high rainfall and the density of saltwater, the surface of Milford Sound is a layer of freshwater containing tannins from the surrounding rainforest. 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, significantly closer to the surface than usual. History 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 was a playground for local Māori who had acquired a large amount of local marine knowledge including tidal patterns and fish feeding patterns over generations prior to European arrival. The fiord remained undiscovered by Europeans until Captain John Grono discovered it c.1812 and named it Milford Haven after his homeland in Wales.