In January, millions of fish died in Australia’s Murray–Darling Basin as the region experienced some of its driest and hottest weather on record. The heat also caused severe water shortages for people living there. Such harsh conditions will become more common as the world warms. Iconic and valuable species such as the Murray cod (Maccullochella peelii peelii) — Australia’s largest freshwater fish — could vanish, threatening biodiversity and livelihoods.

Rivers around the world are struggling to cope with changing weather patterns. In Germany and Switzerland, a heatwave last year killed thousands of fish and blocked shipping on the River Rhine. California is emerging from a six-year drought1 that restricted water supplies and devastated trees, fish and other aquatic life. Across the US southwest, extended dry spells are destroying many more forests and wetlands.