The sudden die-off of more than a hundred Amazonian river dolphins in recent days has prompted fears that rising global heat could be passing the tolerance threshold of species in vulnerable areas.

The floating corpses of the endangered mammals, along with thousands of dead fish, have appeared at Lake Tefé where the temperature is now like a hot bath after a protracted drought has dried up most of the water.

As in other parts of the world, Brazil has suffered from unusually extreme weather in recent months as a consequence of human-caused climate breakdown and an El Niño.

With a widening area affected by water shortages and the drought expected to intensify in October, local officials have travelled to Brasília to petition the federal authorities for humanitarian aid.

Earlier this month, fishers in Marechal Thaumaturgo, Pará state rescued two of the mammals who became trapped when water levels in the Juruá River fell to 2.3 metres, the lowest point in five years.

“This extraordinary species is already endangered – so losing so many individuals in such a short space of time is disastrous.” She said this tragedy required an urgent response and highlighted the importance of the global declaration of river dolphins, which is due to be signed on 24 October.

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