Ayan Santos Fleischmann, Fabrice Papa, Stephen Hamilton, John Melack, Bruce Forsberg, Adalberto Val, Walter Collischonn, Leonardo Laipelt, Júlia Rossi, Bruno Comini de Andrade, Bruna Mendel, Priscila Alves, Maiby Glorize, Lady Custodio, Maria Cecília Gomes, Débora Hymans, Isabela Keppe, Raize Mendes, Renan Gomes, Paula Silva, Camila Vieira, Rodrigo Xavier, André Zumak, Anderson Ruhoff, Wencai Zhou, Sally MacIntyre, Eduardo Martins, Naziano Filizola, Rogério Marinho, Ednaldo Severo, Mariana Frias, Renata Oliveira, Lucas Lauretto, Waleska Gravena, André Coelho, Hilda Perez, Susana Mota, Michel Nasser, Daniel Moreira, Leandro Santos, José Reinaldo Peleja, Miriam Marmontel

In 2023, an unprecedented drought and heatwave severely impacted Amazon waters, leading to high mortality of fishes and river dolphins. Five of 10 lakes monitored showed exceptionally high daytime temperatures (>37°C), with one large lake reaching up to 41°C in the entire ~2-m deep water column, with up to 13°C of diel variation. Modeling show that high solar radiation, reduced water depth and wind speed, and turbid waters are the main drivers of the high temperatures. This extreme heating of Amazon waters follows a long-term increase of 0.6°C/decade revealed by satellite estimates across the region’s lakes between 1990 and 2023. With ongoing climate change, temperatures that approach or exceed thermal tolerances for aquatic life are likely to become more common in tropical aquatic systems.