Each year, between July and October, approximately 1.5 million wildebeest, 400,000 zebras, and 200,000 gazelles migrate through the Maasai Mara in Kenya, chasing the rain and eating the tall grasses as they come from the Serengeti in Tanzania. To return to Tanzania the enormous herds must cross the great divide of the dangerous waters of the Mara River. Arguably this is one of the most astonishing events in nature.