Extreme Heat and Drought Turned Ecosystems Into “Simmering Basins”
A new study has revealed that several lakes in the Amazon Basin became hotter than the maximum safe temperature recommended for hot tubs during the record-breaking heat and drought of 2023, transforming into “shallow, simmering basins” that proved deadly for aquatic life. Researchers say the event underscores how climate change is pushing tropical ecosystems to their limits.
While the world’s lakes are recognized as key indicators of climate change, most studies have focused on temperate regions. Scientists in Brazil have begun filling that gap, analyzing ten Amazon lakes during the extreme weather event in September and October 2023 — when water levels dropped to record lows and temperatures soared.
In half the lakes studied, daytime temperatures exceeded 37°C (98.6°F) — a threshold rarely seen in large natural water bodies. At Lake Tefé, a 37-mile-long lake in northwestern Brazil, temperatures reached an astonishing 41°C (105.8°F) in October 2023, surpassing the 104°F safety limit set by the U.S. Centers for Disease Control and Prevention for hot tubs.
Unprecedented Conditions and Mass Dolphin Deaths
The heat penetrated beyond the lake’s surface, reaching depths of over six feet, leaving no refuge for aquatic life. “Such high temperatures to these depths are likely unprecedented,” said Ayan Fleischmann, a hydrologist at the Mamirauá Institute for Sustainable Development and co-author of the report. “Though we lack long-term observations, it’s clear the event went beyond the thermal tolerance of many species.”
Lake Tefé’s surface area shrank by 75%, while Lake Badajós contracted by 92%. These conditions triggered a catastrophic die-off of aquatic species. At Lake Tefé alone, more than 200 Amazon river and tucuxi dolphins were found dead between late September and October 2023. The study suggests that extreme heat may have impaired the dolphins’ neurological functions, preventing them from seeking cooler waters downstream.
Fish populations also suffered, with more than 3,000 deaths reported at a nearby aquaculture site. For local communities, the crisis was devastating — cutting off access to food, clean water, and medical supplies. “When aquatic ecosystems are disrupted, Amazonian communities are disrupted,” Fleischmann said.
Climate Forces Behind the Heat Disaster
Researchers identified multiple factors behind the extreme warming: prolonged drought that reduced water levels, murky water that absorbed more solar radiation, intense sunlight, and low wind speeds that prevented cooling through evaporation. Together, these conditions created an unprecedented thermal event in the region.
While the study centered on 2023, similar conditions repeated in 2024, when the central Amazon experienced another severe drought — the worst since records began in 1950. These back-to-back disasters highlight the growing instability of the region’s climate systems.
Long-Term Warming Trends Threaten Amazon Lakes
Due to limited long-term data, scientists cannot precisely track how rapidly Amazon lakes are heating, but satellite-based analysis of 24 lakes suggests average surface temperatures have increased by 0.6°C (1°F) per decade over the past 30 years.
“Amazon lakes are facing a long-term warming process, likely associated with climate change and global warming,” Fleischmann warned. The findings serve as a stark reminder that the Amazon, long regarded as a global climate regulator, is increasingly becoming a casualty of the warming planet — with consequences that ripple far beyond its shores.