More than 100 dolphins have been found dead in the Brazilian Amazon amid record-high water temperatures at nearly 40 deg C and a drought.

CNN reported on Sunday that the dolphins had been found dead in Lake Tefe over the past week, according to research facility Mamiraua Institute, which is funded by the Brazilian Ministry of Science.

The Amazon River is one of the world’s longest rivers. At nearly 6,500km long, it weaves through the Amazon rainforest, which is home to a diverse range of wildlife and plants.

A Mamiraua Institute spokesman said: “It’s still early to determine the cause of this extreme event, but according to our experts, it is certainly connected to the drought period and high temperatures in Lake Tefe, in which some points are exceeding 39 deg C.”

Researchers and activists are attempting to transfer surviving dolphins from lagoons and ponds in the outskirts of the Amazon to the main river body, where cooler water is found.

However, the process is difficult due to the remote nature of the area, said the CNN report.

Mr Andre Coelho, a researcher from the institute, added that it is necessary to verify if toxins or viruses are present in other rivers before transferring the dolphins to them.

The drought has also had knock-on effects on the economy, as low water levels reported in 59 municipalities of the Amazonas State have hindered transport and fishing activities in the river.

More dolphins could end up dead in the next few weeks as the drought is expected to worsen, said the Brazilian authorities.