The second episode explores East Africa's rich variety of freshwater and marine habitats. The Rift Valley's seasonal rains replenish a network of rivers which sustain life through the prolonged dry periods. The dry season affects animals differently. Elephants congregate on riverbanks and reinforce social bonds, while bee-eaters arrive to build nest holes in the exposed mud cliffs. For river hippos, it's a time of tension as hundreds of animals jostle for position in the remaining deep water channels. The hippos of Mzima, by contrast, have a guaranteed year-round water supply thanks to the natural volcanic spring. For the first time, cameras film bottom-dwelling crabs and Bathyclarias catfish in the depths of Lake Malawi. In calm conditions, clouds of midges emerge to mate and lay their eggs on the lake's surface. At night, local fishermen trawl for shoals of ucepa, which are drawn to the surface to feed on the midge larvae. Few creatures can survive in the caustic lakes of the Eastern Rift Valley. In Lake Natron, a tilapia swims too close to a thermal vent with fatal results. Aerial shots show the million-strong colony of lesser flamingos on Lake Bogoria. At its northern extreme, the Rift Valley plunges into the Red Sea. The final sequences show the diversity of marine life off the coast of Djibouti, including a group of whale sharks filter-feeding at Ghoubet. Inside the Great Rift shows how a submersible ROV was lowered into a reef crack to capture shots of deep sea life.