Dumb Blonde Swimming

On a deserted island there were three women, a blond a brunette and a redhead. They needed to get back to the mainland and the only way was by swimming. The redhead goes first. She makes it a quarter of the way then drowns. The brunnette goes second. She makes it one third of the way then drowns.The blonde comes last. She makes it one half of the way, gets tired and then turns back.