Freshwater biodiversity, from fish to frogs and microbes to macrophytes, provides a vast array of services to people. These services are under a growing threat as human-related pressure threatens freshwater biodiversity on multiple fronts. Here, Abigail Lynch and colleagues discuss nine fundamental ecosystem services that freshwater biodiversity provide to people. Given the importance of freshwater biodiversity to our very existence, they make a plea for a redoubled effort to better conserve this precious resource.