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."

This very dark, scared up, 21 year old grizzly boar found a bison carcass in the Yellowstone River, in Yellowstone National Park, and fed on it for more than a week. Some estimate that the bear ate around 1000 pounds of meat before he finished. 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.

The bull bison was seen drowning in the river as he was trying to cross to the other side. It is not known if the bison was injured prior to drowning. The carcass sat in the river for ten days, originally in a place that would have been difficult for viewing, before the bear found it and began eating. The carcass then floated downriver to a popular spot for viewing Harlequin ducks and cutthroat trout, LeHardy Rapids, where thousands of park visitors enjoyed watching this bear and a few others that came in to feed.