Dams pose significant threats to the persistence of freshwater fish species globally. A study led by Tamara Keijzer and colleagues assessed the impact of dams on freshwater fish populations, revealing that over half of the 7369 species analyzed face local extinction due to habitat fragmentation. The research developed a global macroecological relationship between fish body size and range size, showing that smaller species require larger areas to persist, while larger species need even more space. The study found that dams, especially small ones, significantly increase the potential loss of fish habitats, with some species losing over 50% of their range. In regions like Brazil, the Mekong basin, and the United States, dams contribute to the fragmentation of fish habitats, increasing the risk of extinction. The study highlights the need for comprehensive dam inventories and strategies to balance hydropower development with biodiversity conservation. The findings emphasize the importance of addressing dam-related threats to protect freshwater fish populations globally.Dams pose significant threats to the persistence of freshwater fish species globally. A study led by Tamara Keijzer and colleagues assessed the impact of dams on freshwater fish populations, revealing that over half of the 7369 species analyzed face local extinction due to habitat fragmentation. The research developed a global macroecological relationship between fish body size and range size, showing that smaller species require larger areas to persist, while larger species need even more space. The study found that dams, especially small ones, significantly increase the potential loss of fish habitats, with some species losing over 50% of their range. In regions like Brazil, the Mekong basin, and the United States, dams contribute to the fragmentation of fish habitats, increasing the risk of extinction. The study highlights the need for comprehensive dam inventories and strategies to balance hydropower development with biodiversity conservation. The findings emphasize the importance of addressing dam-related threats to protect freshwater fish populations globally.