A new study published in Science has revealed chilling details behind the mass death of dolphins in Brazil’s Amazon region, where Lake Tefé turned into what scientists described as a “steaming cauldron” during the 2023 drought and heat wave.
When hydrologist Ayan Fleischmann and his team from the Mamirauá Institute for Sustainable Development arrived at the site, they found lake temperatures reaching 41°C (105.8°F) — hotter than most hot tubs — devastating aquatic life and exposing the deadly effects of climate change on tropical ecosystems.
“You couldn’t put your finger in the water,” Fleischmann told AFP. “The psychological impact of seeing so many dead dolphins was overwhelming.”
The Amazon River dolphins and tucuxis, both endangered and symbolic of the region’s biodiversity, died in unprecedented numbers — 153 carcasses were recovered in just one week of September 2023, including 130 pink dolphins and 23 tucuxis, according to WWF Brazil.
A Lake Turned Into a Death Trap
The research found that Lake Tefé’s surface area shrank by 75% as temperatures surged far beyond the normal 29–30°C range.
Fleischmann’s team recorded similar temperature spikes — above 37°C — in five out of ten Amazonian lakes they studied. Using advanced climate models, the researchers identified four key factors that caused the thermal crisis:
- Strong solar radiation
- Shallow waters
- Low wind speeds
- High turbidity (murky water trapping heat)
These conditions created a “feedback loop”, preventing heat dissipation and effectively cooking aquatic life.
“The climate emergency is here — there is no doubt about it,” Fleischmann said. “These lakes are vital for local livelihoods and biodiversity, but they are heating faster than the global average.”
Beyond the Dolphins: A Wider Ecological Collapse
The dolphins’ deaths were only “the tip of the iceberg.” Thousands of fish also perished, and an algal bloom turned the water blood-red as phytoplankton came under stress — a sign of a collapsing aquatic ecosystem.
NASA satellite data revealed that Amazonian lakes have been warming at roughly 0.6°C per decade since 1990, significantly higher than the global average.
The droughts in 2023 and 2024, both record-breaking, are part of a growing trend of climate-induced extreme events affecting South America’s largest rainforest basin.
Fleischmann plans to present these findings at the UN COP30 climate summit in Brazil, urging world leaders to fund long-term environmental monitoring and involve Indigenous and local communities in restoration efforts.
“We need to listen to the people who live here — they are the first to feel these changes and the last to be heard,” he said.
Scientific Warning
Complementary research published in Hydrological Processes by University of Birmingham professor David Hannah found that droughts dramatically increase river and lake temperatures, causing widespread ecological damage.
“Rising water temperatures can have significant and often detrimental implications for aquatic life, impacting both individual species and entire ecosystems,” Hannah said.
With climate change intensifying, scientists warn that the Amazon’s freshwater ecosystems could face irreversible collapse if global temperatures continue to rise.
