AdvertisementRio's Marathon Swim: A Battle Against Waves, Pollution And JellyfishAugust 04, 2016Melissa BlockfacebookEmailU.S. marathon swimmer Haley Anderson won a silver at the 2012 Olympics when she lost a sprint to the finish by four-tenths of a second. Anderson, 24, will be swimming the 6.2-mile race again in Rio, where much of the pre-race attention has focused on the polluted waters. (NPR)