This episode describes the course taken by rivers and some of the species that take advantage of such a habitat. Only 3% of the world's water is fresh, yet all life is ultimately dependent on it. Its journey begins as a stream in the mountains, illustrated by Venezuela's Tepui, where there is a tropical downpour almost every day. It then travels hundreds of miles before forming rapids. With the aid of some expansive helicopter photography, one sequence demonstrates the vastness of Angel Falls, the world's highest free-flowing waterfall. Its waters drop unbroken for nearly 1,000 metres and are blown away as a mist before they reach the bottom. The erosive nature of rivers is shown by the Grand Canyon, created over five million years by the Colorado River. In Japan, the water is inhabited by the biggest amphibian, the two-metre long giant salamander, while in the northern hemisphere, salmon undertake the largest freshwater migration, and are hunted en route by grizzly bears. Also featured are smooth-coated otters repelling mugger crocodiles and the latter's Nile cousin ambushing wildebeest as they cross the Mara River. Roseate spoonbills are numerous in the Pantanal and are prey to spectacled caiman. In addition, there are cichlids, piranhas, river dolphins and swimming crab-eating macaques.
