A Science study found that a late-2023 heatwave and drought raised temperatures in some Amazon lakes to about 41°C (105.8°F), killing more than 150 endangered river dolphins and thousands of fish. Researchers reconstructed conditions in 10 lakes and identified shallow water, strong solar radiation, low wind and high turbidity as the lethal mix. Heat penetrated up to two meters in Lake Tefé, which researchers described as a "steaming cauldron." Scientists warn the event — repeated in 2024 — may signal a recurring climate-driven threat and call for sustained monitoring and inclusion of local communities.
Study Finds Extreme Heat Turned Amazon Lakes into 'Steaming Cauldrons,' Killing More Than 150 River Dolphins
A Science study found that a late-2023 heatwave and drought raised temperatures in some Amazon lakes to about 41°C (105.8°F), killing more than 150 endangered river dolphins and thousands of fish. Researchers reconstructed conditions in 10 lakes and identified shallow water, strong solar radiation, low wind and high turbidity as the lethal mix. Heat penetrated up to two meters in Lake Tefé, which researchers described as a "steaming cauldron." Scientists warn the event — repeated in 2024 — may signal a recurring climate-driven threat and call for sustained monitoring and inclusion of local communities.
01:31 PM, 11/13/2025Environment
Extreme heat and drought made shallow Amazon lakes lethally hot, study finds
A new peer-reviewed study published in Science shows that an intense late-2023 heatwave combined with severe drought raised temperatures in some central Amazon lakes to roughly 41°C (105.8°F), creating conditions lethal to aquatic life. Researchers recovered more than 150 endangered river dolphins — including pink dolphins (Inia geoffrensis) and tucuxis — from Lake Tefé within a single week.
Lead author and hydrologist Ayan Fleischmann of the Mamirauá Institute for Sustainable Development described Lake Tefé during the event as "a steaming cauldron." Field measurements indicated surface temperatures comparable to hot springs, with heat penetrating the lake down to two meters. "You couldn't put your finger in the water," Fleischmann told AFP, as reported by CBS News.
The team reconstructed water conditions in 10 central Amazon lakes and identified a deadly combination of factors: shallow depth, strong solar radiation, low wind, and high turbidity (murky, sediment-rich water that retains heat). Over the past three decades, Amazonian lakes have warmed at an estimated rate of about 0.6°C per decade — faster than the global average — making them more vulnerable to extreme events.
Beyond the dolphins, thousands of fish died, disrupting food supplies for riverside communities. Researchers also documented a stress-driven bloom of red algae in Lake Tefé, a sign of ecosystem collapse. Similar patterns of drought and extreme heat recurred in 2024, prompting scientists to warn that such mass-mortality events may become more frequent as the climate warms.
"The climate emergency is here — there's no doubt about it," Fleischmann said. He will present the findings at COP30 in Brazil and researchers are calling for long-term monitoring of Amazonian lakes and closer involvement of Indigenous and riverine communities in conservation planning.
Environmental groups, including the World Wildlife Fund, condemned the die-off as "appalling" and said it foreshadows broader risks to the region's wildlife and the livelihoods of local people. Scientists emphasize that the mass deaths are not an isolated tragedy but a warning that even remote freshwater ecosystems are increasingly vulnerable to extreme heat.
Photo credit: REUTERS/Bruno Kelly; research published in Science.