PLANET EARTH Freshwater

Up here, there are fewer predators to eat their eggs and fry（这里表示鱼苗）. A grizzly bear. From famine to feast - he's spoilt for choice. This Canadian bear is very special - he's learnt to dive for his dinner. But catching salmon in deep water is not that easy and the cubs have lots to learn. The annual arrival of spawning salmon brings huge quantities of food into these high rivers that normally struggle to support much life.



Although relatively lifeless, the power of the upland rivers to shape the landscape is greater than any other stage in a river's life. Driven by gravity, they're the most erosive（侵蚀性的） forces on the planet. For the past 5 million years Arizona's（亚利桑那州（美国西南部的州）） Colorado（科罗拉多） river has eaten away at the desert's sandstone to create a gigantic（庞大的） canyon. It's over a mile deep and at its widest it's 17 miles across. The Grand Canyon（大峡谷，地名）. This river has cut the world's longest canyon system - a 1,000 mile scar clearly visible from space.