It’s the largest animals who tend to occupy the most space in our hearts. They might be imperiled—indeed they usually are, as it’s not easy being big in a human-dominated world—but at least people know and care. There’s one group of large animals, however, whose decline has gone mostly unremarked: those who live in lakes and streams and rivers.

“Globally, freshwater megafauna populations declined by 88 percent from 1970 and 2012,” write biologists led by Fengzhi He and Sonja Jähnig, both of Germany’s Leibniz Institute of Freshwater Ecology and Inland Fisheries, in the journal Global Change Biology. “Compared to megafauna in terrestrial or marine realms, they have received much less research, conservation efforts, and public attention.”