S1, E2: A spectacular natural event takes place in North America every year as hundreds of millions of salmon return from the Pacific Ocean to the mountain streams where they were born. The salmon must overcome fierce torrents and leap over waterfalls as they make their way upstream. The great run not only provides food for bears, but for killer whales, wolves, bald eagles and even for the forest itself. A family of bears is filmed from the air as they make a treacherous journey to the coast to await the return of the salmon.