Amazing footage has emerged of a grizzly bear eating a bison carcass in a river in Yellowstone National Park, Wyoming, USA.

The video, shot late last month, shows the 21-year-old bear feasting on the carcass of a bison that had drowned in the river.

The filmer wrote online: ''The bear found a bison carcass in the Yellowstone River, in Yellowstone National Park, and fed on it for more than a week."

"At times, the bear looked so stuffed he could barely walk and he often slept on the carcass to keep it safe from other bears or wolves."