Return to the Water

S1, E7: From the roughest seas to the crystal clear waters of the Florida springs, David Attenborough swims with sea otters and dives with manatees, as he follows those mammals who, millions of years ago, left dry land and returned to the water to feed. Attenborough races across the Pacific Ocean to find the largest mammal that has ever lived on this planet, the blue whale, a hundred feet long - thirty metres.