Cold blamed for Bolivia's mass fish deaths

Anna Petherick in Nature News: With high Andean peaks and a humid tropical forest, Bolivia is a country of ecological extremes. But the unusually low winter temperatures experienced by the country's tropical region in July and August hit freshwater species hard, killing an estimated 6 million fish and thousands of alligators, turtles and river dolphins.

Scientists who have visited the affected rivers say the event is the biggest ecological disaster Bolivia has known. They are now scrambling to coordinate research into how it happened, and how quickly the ecosystem may recover. … Decomposing fish have polluted the waters of the Grande, Pirai and Ichilo rivers so badly that local authorities have had to provide alternative sources of drinking water for towns along the rivers' banks.

The blame lies with a mass of Antarctic air that settled over the Southern Cone of South America for most of July. Water temperatures in Bolivian rivers that normally register about 15 °C during the day fell as low as 4 °C.

"It is not unlikely that the extreme weather conditions in July might have been related to the El Niño–Southern Oscillation [ENSO]," says Fons Smolders, a fisheries scientist at Radboud University in Nijmegen, the Netherlands. "Although it is still debated whether ENSO is affected by climate change, it is generally accepted that climate change has the potential to increase the prevalence and severity of extremes such as heat waves, cold waves, storms, floods and droughts….

Fish farming in Lake Titicaca, Bolivia, shot by Christopher Walker, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license