Published on Nov. 12, 2025, 3:47 PM
The authors are calling for better monitoring of tropical lakes, which are home to countless endangered species and are particularly vulnerable to climate change.
A prolonged drought and heat wave in September 2023 turned lakes in Brazil’s Amazonas state into “shallow simmering basins” with water temperatures above 40ºC — hot enough to kill more than 200 endangered river dolphins, along with thousands of fish and other aquatic species.
“You couldn’t put your finger in the water,” Ayan Fleischmann, the study’s lead author and a hydrologist at western Brazil’s Mamiraua Institute for Sustainable Development, told AFP.
The authors say the event highlights a “worrisome warning trend” across rivers and lake basins, especially for those in the Amazon, which are poorly monitored and understudied.
Intense water temperatures
The findings are detailed in a paper published last week in the journal Science.
For their study, Fleischmann and colleagues analyzed temperatures from 10 central Amazonian lakes during the September 2023 and an October 2024 drought, supported by satellite data and computer models. They found that 5 of the lakes experienced “exceptionally high” daytime temperatures exceeding 37ºC. In the shallow waters of Lake Tefé, temperatures climbed to 41ºC.
In 2024, Lake Tefé lost 75 per cent of its area, and Badajós Lake decreased by 90 per cent.