Hundreds of millions of Pacificsalmon return to the mountain streams in which they were born, where they will spawn and then die. Their passage upstream is fraught with danger, from rapids, waterfalls and hungry grizzly bears. The programme begins at the arrival of spring, with a grizzly mother leading her cubs down from their winter den in the Alaskan mountains. The bears congregate in the forested valleys, where they forage for whatever food they can find. Survival is tough for all, as shown by a pack of hungry wolves attacking an adult grizzly. It is not until July that the salmon arrive in great numbers. Other predators join the feast, including Orcas, Stellar sea Lions, Salmon sharks and the Bald headed Eagle. Those that make it past the bears risk becoming trapped in shallow reaches as the water level subsides. Relief comes as a summer storm replenishes the streams, triggered by moist ocean air rising over the coastal mountains. As they reach the spawning grounds, the salmon change body shape and colour in preparation for spawning. When it is over, the fish are close to exhaustion and they die en masse, providing an easy meal for birds and lingering bears. Their deaths are not in vain, for the nutrients from their decaying bodies help to fertilise the soil, sustaining the forests of tall pines