Amazonian lakes are turning into boiling pools hotter than spa baths as intense heatwaves and drought grip the region, research suggests.
Temperatures at one lake topped 40C (104F) as water levels plummeted under bright sunshine and cloudless skies. The extreme heat has led to mass deaths of endangered dolphins and Amazon fish that cannot survive such high temperatures.
The shallow water of Lake Tefe, which was only two meters deep, reached 41°C – warmer than a regular hot tub. “We couldn't even put our toes in the water. It was very hot, not only at the top, but all the way to the bottom,” said lead researcher Ayan Fleischmann from the Mamiraua Institute for Sustainable Development. “You put your finger in and immediately remove it, it’s unbearable.”
Floating corpses of up to 200 river dolphins it washed out over a six-week period around September 2023. No one in the region has seen this happen in the last century, Fleischmann said. “It was completely surreal and very scary.”
This incident prompted them to look at other bodies of water in the Amazon region. According to the study, half of the 10 lakes studied experienced exceptionally high daytime water temperatures exceeding 37°C. study published in the journal Science.
Researchers analyzed water temperatures in lakes in the central Amazon during the 2023 drought, which was followed late last year by another severe drought with new record low water levels and intense heating of lakes. The average temperature of Lake Tefe in the hottest months reaches 30°C, but in 2024 it reached 40°C.
Amazon lakes have warmed by 0.3 to 0.8 degrees Celsius every decade over the past 30 years or so—a rate faster than the global average, the researchers found. At the same time they are shrinking. During the 2024 drought Lake Tefe has lost about 75% of its area. and Lake Badajoz has shrunk by 90%.
Adrian Barnett, senior lecturer in behavioral ecology at the University of Greenwich, who was not involved in the study, said: “The work shows the extraordinary impact of climate change even on huge ecosystems like the Amazon, and that it is not limited to forests, but also to the aquatic realm.”
“A 10-degree increase in water temperature is unprecedented,” he said. “The amount of energy required to achieve this in such huge volumes of water is amazing.”
Most fish, as well as dolphins and manatees, typically breed during low water periods, Barnett said, adding that it is likely that 2023 will be a reproductive disaster for most species. “If this happens repeatedly, their populations and the species associated with them ecologically will be greatly reduced.”
There are several local solutions to this problem, Barnett said. “What's happening on such a huge scale really requires a systems approach, and that means tackling the root cause of the problem, which is fossil fuel emissions and the causes of global warming itself,” he said.
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