The Mara river, snaking across the plains of East Africa. As the land flattens out rivers slow down and lose their destructive power. Now they're carrying heavy loads of sediment that stains their waters brown. Lines of wildebeest are on the march. Each year nearly 2 million animals migrate across the Serengeti plains in search of fresh green pastures. For these thirsty herds the rivers are not only a vital source of drinking water, but also dangerous obstacles. This is one of the largest concentrations of Nile crocodiles in Africa, giants that grow over five metres long. From memory, the crocodiles know the wildebeest are coming and gather in anticipation.


马拉河蜿蜒流过非洲东部的平原。进入平缓地带以后，河流减慢了速度，同时也失去了破坏力。此时它们夹带着大量沉积物，河水也因此变得混浊。角马们正在匆忙赶路。每年大约有200万只动物为追逐新鲜草场而路过塞伦盖蒂草原。对于这些干渴的动物们来说，河流一方面给它们提供至关重要的饮用水，但同时又充满危险。 这里是尼罗鳄在非洲最集中的地方，这种鳄鱼体长可达5米。尼罗鳄凭记忆知道，角马快要来了，于是它们预先集中起来。