Video provided by the institute showed vultures picking at the dolphin carcasses beached on the lakeside. Thousands of fish have also died,local media reported.
Experts believe high water temperatures are the most likely cause of the deaths in the lakes in the region. Temperatures since last week have exceeded 38 degrees Celsius in the Tefe Lake region.
The Brazilian government’s Chico Mendes Institute for Biodiversity Conservation,which manages conservation areas,said last week it had sent teams of veterinarians and aquatic mammal experts to investigate the deaths.
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There had been some 1400 river dolphins in Tefe Lake,said Miriam Marmontel,a researcher from the Mamiraua Institute.
“In one week we have already lost around 120 animals between the two of them,which could represent 5 to 10 per cent of the population,” said Marmontel.
Workers have recovered carcasses of dolphins since in a region where dry rivers have impacted impoverished riverside communities and stuck their boats in the sand. Amazonas Governor Wilson Lima declared a state of emergency on Friday due to the drought.