Nature Climate Change, Published online: 24 August 2026; doi:10.1038/s41558-026-02731-9Assessing 9,809 freshwater fish species globally, this study shows risk to a high proportion of species in the tropics, and severe extremes in non-tropical regions. Under high emissions, gradual warming drives abrupt exposure, with 63% of species facing accelerating thermal fragmentation by 2099.