"You couldn't put your finger in the water," said the lead author of the study, which spotlights the impacts of planetary warming on aquatic ecosystems.

When dolphins began washing up dead by the dozens on Lake Tefe in Brazil’s Amazonas state, hydrologist Ayan Fleischmann was sent to find out why.

What he and his colleagues discovered was startling: a brutal drought and extreme heat wave that began in September 2023 had transformed the lake into a steaming cauldron. The lake’s waters reached 41 degrees Celsius, or 105.8 degrees Fahrenheit — hotter than most spa baths.

Their findings, published Thursday in the journal Science, spotlight the impacts of planetary warming on tropical regions and aquatic ecosystems, and come as the United Nations’ COP30 climate talks kick off in Brazil.