Amazon lakes turned to simmering basins, killing endangered animals
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.
Low wind added to the problems
The authors say the combination of low water levels from the drought, solar heating, calm winds, and high turbidity created the catastrophic conditions in Amazonian lakes.
“The findings suggest that low wind speeds were likely the most critical driver of extreme warming, more so than air temperature itself,” the authors write in a statement.
“With little wind, less heat was lost through evaporation and nighttime cooling, allowing lakes to grow progressively hotter under intense sunlight and persistent clear skies.”
Deforestation in the Amazon is likely compounding drought issues.
A separate and unrelated study from April 2025 found that extensive tree removal in the Amazon forest is causing a significant decrease in rainfall.
Researchers found that a 1 per cent loss of forest coverage led to an estimated 1.69 per cent reduction in precipitation between June and August, Brazil's dry season.
Lakes continue to warm
Climate change is fueling a steady increase in Amazonian lake temperatures, with waters warming between 0.3 to 0.8 ºC per decade.
“Although this study presents data from 2023, in September and October of 2024, another extreme drought occurred in the central Amazon,” the study says, “with new record-breaking low water levels and severe lake water heating associated with hydrological and meteorological conditions similar to those observed in 2023.”
The authors are calling for better monitoring of tropical lakes, which are home to countless endangered species and are particularly vulnerable to climate change.
"The climate emergency is here, there is no doubt about it," Fleischmann told AFP.
Header image: File photo of a rare pink dolphin in the Amazon’s Negro River. (Canva Pro)