How extreme heat and drought devastated Amazon lakes
Researchers say a late-2023 heatwave combined with an unusually dry season turned some central Amazon lakes into lethal environments for aquatic life, killing more than 150 endangered river dolphins and thousands of fish in just days.
A study published in the journal Science examined water conditions across 10 lakes in Brazil's central Amazon and found surface temperatures approaching 41°C (about 105.8°F). At Lake Tefé, those high temperatures persisted through the full two-meter water column, creating conditions that were unsafe for dolphins and many other species.
What the researchers found
The team identified a dangerous combination of factors that trapped heat in shallow lakes: intense solar radiation, very shallow water, low wind, and high turbidity (murky, sediment-rich water that absorbs and retains heat). Hydrologist Ayan Fleischmann of the Mamirauá Institute for Sustainable Development—lead author of the study—described Lake Tefé during the event as "a steaming cauldron." He noted recorded temperatures matched those of hot springs and that locals reported, "you couldn't put your finger in the water."
"The climate emergency is here—there’s no doubt about it," Fleischmann said, noting the event will be presented at COP30 to advocate for sustained monitoring and community-involved conservation.
Broader impacts
Beyond the dolphins (including endangered pink dolphins and tucuxis), thousands of fish died, disrupting food supplies and livelihoods for riverside communities. Researchers also documented a stress-related bloom of red algae in Lake Tefé—an indicator of ecological collapse. The same pattern of extreme drought and heat reappeared in 2024, raising concerns that such mass die-offs could become more frequent.
Long-term trends heighten the risk: over the past three decades Amazonian lakes have warmed by roughly 0.6°C per decade—faster than the global average—making these ecosystems more vulnerable when heatwaves and droughts coincide.
What scientists recommend
The authors urge long-term monitoring of Amazonian lakes, stronger inclusion of Indigenous and riverine communities in conservation planning, and broader climate mitigation efforts. Environmental organizations, including the World Wildlife Fund, called the die-off "appalling" and a warning of future threats to the region's wildlife and people.
Bottom line: The mass mortality is not an isolated tragedy but a clear signal that even remote freshwater habitats in the world's largest rainforest are increasingly exposed to lethal heat driven by climate change.
