Arriving with a splash, an adult hippo enters the waters of the OKavango Delta in Botswana. Hippos are rarely seen out of the water during the day, preferring to graze on land at night. The Okavango Delta is a world heritage site and home to many of the most iconic large mammals left on Earth, including the largest herd of elephants in the world. It is also a vital lifeline for almost a million people.