Flooding and dam operations facilitate rapid upstream migrations of native and invasive fish species on a regulated large river.

Dams commonly restrict fish movements in large rivers but can also help curtail the spread of invasive species, such as invasive bigheaded carps (Hypophthalmichthys spp). To determine how dams in the upper Mississippi River (UMR) affect large-scale invasive and native fish migrations, we tracked American paddlefish (Polyodon spathula) and bigheaded carp across > 600 river km (rkm) and 16 navigation locks and dams (LD) of the UMR during 2 years with contrasting water levels. In 2022, a low-water year, both native paddlefish and invasive bigheaded carp had low passage rates (4% and 0.