More than 200 dolphins died in Lake Tefé during the historic drought of 2023 in the Amazon: this was confirmed by a study published in the Science journal.
At the time, the waters reached record temperatures of 41 degrees, a lethal level for the aquatic fauna of the region.
The research, led by Brazilian scientist Ayan Fleischmann from the Mamirauá Institute for Sustainable Development, analyzed ten lakes in the central Amazon.
In five of them, the water exceeded 37 degrees Celsius.
“It was impossible to put a finger in the water. It was so hot that the animals had no refuge,” explained Fleischmann.
Lake Tefé recorded 41 degrees throughout its water column, just two meters deep.
The researcher described the phenomenon as “a perfect storm.”
This included extreme solar radiation, shallow depth, weak wind, and turbid waters that prevented heat dispersion.
The crisis did not only affect the Amazon dolphins
The mass mortality was not limited to dolphins. Fish, phytoplankton, and other aquatic organisms also died due to the extreme temperatures.
“The lake turned a red color due to the algae that changed their pigmentation,” noted the scientist.
According to Dr. Adalberto Val from the Brazilian Amazon Research Institute (INPA), most Amazonian organisms are extremely sensitive to heat.
“When the water reaches 41 degrees, the fish simply stop functioning: their enzymes get blocked, their metabolism collapses and they die,” he explained.
The Amazon dolphins, capable of regulating their body temperature, could not withstand it either.
“They have to expend a huge amount of energy to stay alive, and in a depleted environment, without food or shelter, they cannot sustain that effort,” detailed Val.
Additionally, Lake Tefé itself lost 75% of its area, shrinking from 400 to 100 square kilometers.
Its depth also reduced from thirteen meters to half a meter.
Drought and global warming: a recurring pattern in Brazil
The Amazon region records a sustained warming of 0.6 °C per decade since 1990, driven by deforestation and global climate change.
“The lakes have been continuously warming over the past decades, and when that trend is combined with an extreme drought, it creates the ideal conditions for even more intense heatwaves,” detailed Fleischmann.
The 2023-2024 drought was the largest ever recorded in at least 120 years, according to available hydrological data.
Núria Bonada, professor of Ecology at the University of Barcelona, warned that “around 60% of the world’s river network suffers droughts every year.”
Furthermore, she left a harsh warning for the future: “And everything indicates that they will be more frequent and prolonged.”
In 2024, Brazil managed to reduce Amazon deforestation to 5,796 km², an 11% decrease from the previous year.
This is the best figure in over a decade under the government of Luiz Inácio Lula da Silva.
Therefore, despite the critical outlook, Fleischmann remains hopeful.
“In Lake Tefé, 200 dolphins died, but there are thousands of lakes where this did not happen. There is still time to change and prevent this from happening again,” he considered.
