Wildebeest and zebra herds mass, over and over, to cross the Mara River from Tanzania into Kenya during the Great Migration.
Danger lies ahead and they are apprehensive. This is the area where crocs and hippos lay wait under the water. Even the water current can kill the young. Once animals make it across, they are in mortal danger of being trampled or breaking bones as they try to get to the top of the bank. Those that make it out face a final hurdle--lions stalk the edge looking to pick off the young, weak or injured.