Amazon River Dolphins Are Facing Mass Die-Offs In Brazil

Brazilian scientists worry that a few straight days of intense sun could be all it takes to trigger the next die-off of the endangered dolphins.

TEFÉ, Brazil — Each morning for the last several weeks, researcher Miriam Marmontel has gazed out at Lake Tefé and the Amazon River, through a thick curtain of smoke from thousands of wildfires raging throughout the region, with a sense of dread and déjà vu.

Brazil is in the grip of severe drought for the second time in as many years — this one already topping 2023 as the worst, most widespread drought in Brazil’s recorded history. Major rivers throughout the Amazon Basin have plummeted to record low levels, and water temperatures are approaching those that triggered mass die-offs of two species of endangered river dolphins this time last summer.

A year ago, drought drove water temperatures in Lake Tefé, in the northern Brazilian state of Amazonas, to as high as 105 degrees Fahrenheit — the upper threshold of a hot tub. By late September, the pink and gray carcasses of freshwater dolphins began washing ashore in large numbers.

“It was really horrible to see. We saw them dying in front of us,” recalled Marmontel, an aquatic mammal expert at the Tefé-based Mamirauá Institute for Sustainable Development.

Now she and a team of researchers at the Mamirauá Institute are bracing for what they fear could be even more extreme and deadly conditions. Drought arrived in the Amazon a month earlier than usual this year. In Tefé, water levels have been dropping by as much as 1 foot per day, turning areas that were recently covered in water into bone-dry expanses of sand. As of Thursday, water levels on the lake were only 8 to 12 inches above last year’s record lows, according to Ayan Fleischmann, a hydrologist at the Mamirauá Institute. Upstream of Tefé, water levels on many rivers have already smashed record lows set last year.