MANAUS --- The carcasses of 120 river dolphins have been found floating on a tributary of the Amazon River since last week in circumstances that experts suspect were caused by severe drought and heat. Low river levels during a severe drought have heated water in stretches to temperatures that are intolerable for the dolphins, researchers believe. Thousands of fish have died recently on Amazon rivers due to a lack of oxygen in the water. The Amazon river dolphins, many of a striking pink color, are unique freshwater species found only in the rivers of South America and are one of a handful of freshwater dolphin species left in the world. Slow reproductive cycles make their popul...Keep on reading: Mass death of Amazon river dolphins linked to severe drought, heat