More than a hundred dolphins have been found dead in the Brazilian Amazon amid an historic drought and record-high water temperatures that in places have exceeded 102 degrees Fahrenheit [38.8 °C].

The dead dolphins were all found in Lake Tefé over the past seven days, according to the Mamirauá Institute, a research facility funded by the Brazilian Ministry of Science.

The institute said such a high number of deaths was unusual and suggested record-high lake temperatures and an historic drought in the Amazon may have been the cause.

The news is likely to add to the concerns of climate scientists over the effects human activity and extreme droughts are having on the region.