Study finds record warming in Amazon lakes during 2023–24 droughts, triggering mass die-offs of fish and river dolphins and threatening freshwater ecosystems

An unprecedented heatwave and drought in 2023 turned several of the Amazon’s lakes into near-boiling basins, with temperatures soaring above 40 degrees, according to a new study by researcher Ayan Fleischmann and colleagues. The extreme conditions led to mass fish die-offs, the death of endangered Amazon River dolphins, and isolation of riverine communities as water levels plunged.

The study, which analysed temperature data from ten central Amazonian lakes, revealed how severe drought and intense solar radiation combined to create “lake heat waves” extreme warming events where water temperatures rose far beyond seasonal norms. In one instance, Lake Tef recorded temperatures of 41 degrees across its two-metre depth.

Researchers attributed the phenomenon to a mix of low water levels, calm winds, and high turbidity that prevented normal heat dissipation through evaporation and night-time cooling. Satellite observations and hydrodynamic modelling confirmed that these conditions trapped heat near the surface, pushing aquatic ecosystems to dangerous limits.

The findings also point to a long-term warming trend, with Amazon lakes heating at a rate of 0.3 to 0.8 degrees per decade over the past 30 years — faster than the global average. The situation worsened in 2024 when another severe drought hit, shrinking Lake Tef by 75 per cent and Lake Badajos by 90 per cent.

Amazon Ecosystems Under Strain
Scientists warned that tropical freshwater systems are reaching a critical threshold. As forests around the lakes continue to thin, surface heating intensifies, reducing shade and oxygen levels vital for aquatic life. The study underscored that tropical lakes, which are crucial for biodiversity and livelihoods, remain understudied despite being highly sensitive to climate shifts.

The broader Amazon basin is also under stress. Reports show tropical primary forests lost 6.7 million hectares in 2024, while deforestation levels have not meaningfully declined despite global commitments. With recurring droughts and record-low river levels, the region faces compounding threats of ecosystem collapse and community displacement.

Researchers caution that the Amazon’s lakes long regarded as sentinels of climate change are now sending a stark warning, the world’s largest rainforest is entering a dangerous new phase of ecological instability.