Cold waves crossing the Amazon rainforest are an extraordinary phenomenon likely to be affected by climate change. We here describe an extensive cold wave that occurred in June 2023 in Amazonian–Andean forests and compare environmental temperatures to experimentally measured thermal tolerances and their impact on lowland animal communities (insects and wild mammals). While we found strong reductions in activity abundance of all animal groups under the cold wave, tropical lowland animals showed thermal tolerance limits below the lowest environmental temperatures measured during the cold wave. While mammal activity and the biomass of most insects recovered over the next season, dung beetle biomass remained low. A quarter of all insects showed very small thermal safety margins (0.62 °C) with respect to the recorded minimum temperature of 10.5 °C, suggesting that an increased intensity of cold waves in the future could imperil cold-sensitive taxa of Amazonian animal communities.