NEED TO KNOW
- In 2023, Amazon lakes reached deadly temperatures above 105°F, killing over 150 dolphins, a new study confirms
- Extreme drought, shallow waters, and high turbidity created lethal conditions for aquatic life and led to the mass dolphin die-off
- Researchers warn that such events are increasing with climate change, threatening local ecosystems
Researchers have an answer as to how dozens of dolphins were killed seemingly overnight in one of the most biodiverse regions on Earth — and it points squarely to the growing dangers of extreme heat in the Amazon.
A study published earlier this month in Science confirms that record-breaking temperatures and a severe drought in late 2023 created deadly conditions across Brazil’s central Amazon, effectively turning some lakes into hot tubs.
The water in Lake Tefé, once a refuge for wildlife and local fishers alike, reached a staggering 41°C (105.8°F), a temperature unsafe for aquatic life. Within a week, more than 150 endangered river dolphins — including both pink dolphins and tucuxis — were found dead in Lake Tefé.
The study’s findings reveal how climate change is reshaping even the most remote ecosystems. Over the past three decades, scientists have found that Amazonian lakes have warmed at a rate of approximately 0.6°C per decade, which is higher than the global average.
When 2023’s intense heatwave collided with one of the driest seasons on record, vast areas of the Amazon’s waterways shrank or dried up entirely, concentrating heat in the shallow lakes that remained.
Hydrologist Ayan Fleischmann, of the Mamirauá Institute for Sustainable Development and the study’s lead author, described Lake Tefé during this period as “a steaming cauldron.” His team recorded surface temperatures that not only matched those of hot springs but also permeated the full two-meter depth of the lake.
“You couldn’t put your finger in the water,” he told AFP, per CBS News, recalling the impact the soaring temperatures had on the dolphins and the local communities around the lake.
For the study, researchers reconstructed water conditions across 10 central Amazon lakes to determine the cause of the dolphins’ deaths in 2023. The team identified a deadly mix of drivers: strong solar radiation, shallow water, little wind, and high turbidity — meaning murky, sediment-filled water that traps heat.
Beyond the dolphins, thousands of fish perished, disrupting food supplies for riverside families. In Lake Tefé, researchers also documented a stress-induced bloom of red algae, a symptom of the ecosystem’s collapse. The same pattern of extreme drought and heat repeated in 2024, signaling what scientists warn could become a recurring cycle.
“The climate emergency is here — there’s no doubt about it,” Fleischmann stated. He plans to present the findings at COP30, the upcoming United Nations climate summit in Brazil, where researchers aim to advocate for long-term monitoring of Amazonian lakes and increased inclusion of Indigenous and riverine communities in conservation efforts.
Environmental organizations have echoed that same sentiment of urgency. The World Wildlife Fund called the dolphin die-off “appalling” and a sign of what’s to come for the region’s wildlife and its people.
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The mass mortality, scientists say, is more than an isolated tragedy. It’s a warning from the world’s largest rainforest — a vivid sign that even its deepest waters are no longer safe from the heat.
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