Lakes in the Amazon became hotter than the maximum temperature recommended for hot tubs as unprecedented heat and drought in 2023 turned them into “shallow, simmering basins,” according to a new study — and it proved a death sentence for endangered dolphins.The world’s lakes are considered sentinels of climate change and are warming dramatically as global temperatures rise. Research, however, has tended to focus on temperate lakes rather than those in the tropics, despite their huge vulnerability to intense warming.Scientists in Brazil are trying to fill some of these gaps. They used satellite data to analyze 10 Amazon lakes during a devastating climate change-driven heat wave and drought in September and October 2023, which pushed them to the lowest water levels on record at the time.AdvertisementAdvertisementAdvertisementAdvertisementIn half the lakes, daytime temperatures were “exceptionally high,” above 37 degrees Celsius (98.6 Fahrenheit), according to the research published Thursday. These kinds of temperatures are rare in large bodies of water — even in tropical regions. Daytime temperatures in Amazonian lakes are more typically around 30 degrees Celsius (86 Fahrenheit).Lake Tefé, a roughly 37-mile long lake in northwestern Brazil, endured especially intense heat.A dead dolphin at Lake Tefé which flows into the Solimões River, in the city of Tefé, Amazonas state, Brazil, October 1, 2023. – Bruno Kelly/ReutersDaytime temperatures in the lake spiked to 41 degrees (105.8 Fahrenheit) in October 2023 — hotter than the average spa bath, and exceeding the 104 degrees Fahrenheit limit the US Centers for Disease Control and Prevention recommends for hot tubs.Strikingly, this heat was not just on the surface but was also detected at depths of more than 6 feet, leaving nowhere in the lake for fish and dolphins to take refuge.AdvertisementAdvertisementAdvertisementAdvertisementSuch high temperatures to these depths are “likely unprecedented, though, we lack long-term observations” to understand what happened in the past, said Ayan Fleischmann, a report author and hydrologist at the Mamirauá Institute for Sustainable Development in Brazil.Many of the lakes also shrunk dramatically. Lake Tefé’s surface area decreased by 75%, while another lake, Badajós, shrunk by 92%.The impacts of the extreme heat were severe. The temperatures went “beyond the thermal tolerance of many aquatic animals,” Fleischmann told CNN. It led to an unprecedented mass die off of Amazon river and tucuxi dolphins, the report found.At Lake Tefé, more than 200 bodies of freshwater dolphins were found between late September and October 2023. It’s not fully known why the dolphins stayed in the hot lake and didn’t seek cooler water downstream towards the Amazon River, but it’s possible the intense heat affected their brains, the study notes.AdvertisementAdvertisementAdvertisementAdvertisementThe temperature spike …
