Anadromous forage fish, which spawn in freshwater but spend much of their lives at sea, are an important food source for many species. They also play a major role in how freshwater ecosystems function. Despite their importance for ecosystems, many of these fish exist at only a tiny fraction of their previous populations. Writing in BioScience, Steven Mattocks of the University of Massachusetts, in Amherst, and his colleagues outline the effects of lost habitat and river connectivity for these crucial fish.