Major drought and heating of Tefé Lake waters in 2023, reaching >40°C in the entire water column at the monitoring site. Credit: Science (2025). DOI: 10.1126/science.adr4029

During a severe drought and heat wave in 2023, Amazonian lakes reached their highest recorded temperatures. Water temperatures in some areas climbed to an astonishing 41 degrees Celsius (105.8 degrees Fahrenheit) and resulted in the deaths of thousands of aquatic animals, including dozens of river dolphins.

Scientists have long known that the Amazon is heating up, but the extreme 2023 event, triggered by the worst drought on record, created lethal water conditions for some wildlife. The sight of more than 200 floating carcasses of freshwater dolphins in Lake Tefé prompted researchers to study water bodies across the Amazon immediately.

The team, led by Ayan Fleischmann from the Mamirauá Institute for Sustainable Development in Brazil, conducted in situ measurements of 10 Amazonian lakes during the 2023 drought and analyzed satellite data from 24 lakes to assess warming trends over three decades. Additionally, the scientists ran hydrodynamic computer models to determine the exact causes of the extreme heat.

Life-threatening temperatures

Temperatures in five of the ten lakes monitored exceeded 37 degrees Celsius (98.6 degrees Fahrenheit), according to the study published in the journal Science. There were also large daily temperature swings of up to 13 degrees Celsius (23.4 degrees Fahrenheit), which placed extreme thermal stress on fish and other aquatic animals.

Modeling revealed that a perfect storm of conditions caused this environmental disaster. They were high solar radiation, extremely low water depth, murky water (which absorbed rather than reflected sunlight) and low wind speeds.

Unfortunately, the heat reached all the way to the bottom of Lake Tefé, so dolphins and fish couldn’t escape it. The 2023 drought also occurred amid a general warming of the Amazonian lakes. According to the researchers, temperatures have increased by 0.6 degrees Celsius per decade over the last three decades.

A warning for the future

As climate change shows no signs of slowing down, life-threatening temperature extremes may well become more common. “These observations highlight the major threats that will likely affect the people and biodiversity of the Amazon and other tropical waters in the years to come,” wrote the researchers in their paper.

Therefore, the study authors warn that urgent action is needed to monitor and protect these vulnerable areas. “The development of consistent, long-term environmental monitoring of vulnerable lake ecosystems such as Tefé and Coari lakes is imperative for them to be effective sentinels of climate change and to develop management strategies of value to the inhabitants of the region.”

Written for you by our author Paul Arnold, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You’ll get an ad-free account as a thank-you.

More information: Ayan Santos Fleischmann et al, Extreme warming of Amazon waters in a changing climate, Science (2025). DOI: 10.1126/science.adr4029

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Citation: Water temperatures in Amazonian lakes rise to unprecedented levels, killing wildlife (2025, November 8) retrieved 8 November 2025 from https://phys.org/news/2025-11-temperatures-amazonian-lakes-unprecedented-wildlife.html

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