A third killer whale has been found dead in Alaska\'s Nushagak River, the National Oceanic and Atmospheric Administration said.NOA spokeswoman Julie Speegle told Anchorage\'s KTUU-TV the young orca\'s carcass was found Friday near an island in the river near Dillingham by a person who lives in the area.Two adult killer whales were found dead in the river Oct. 8. A necropsy revealed one of them had been pregnant.The three whales had spent about three weeks swimming in the coastal river.