In rivers worldwide, dams, weirs and tidal barrages impede the upstream spawning movements of anadromous lamprey, with subsequent impacts on population viability. Fishways are commonly used to mitigate the impact of barriers on fish migration, but the utility of these structures for southern hemisphere lamprey (e.g. Geotria australis and Mordacia mordax) remains largely unexplored. In this study we implanted PIT (passive integrated transponder) tags into 55 pouched lamprey (Geotria australis) near the mouth of the River Murray, Australia, and assessed upstream passage through a series of vertical slot fishways on 10 main channel weirs (~3.5 m height), across 800 km of river. The fishways comprised two different designs: 1) 1:32 slope, 0.3 m slot width, 1.4 m/s maximum water velocity and turbulence of 47 W/m3; and 2) 1:22 slope, 0.3 m slot width, 1.7 m/s maximum water velocity and turbulence of 87 W/m3. A total of 25 lamprey ascended one or more fishways, with 133 successful ascents recorded across the ten fishways. We compare the two fishway designs with regards to passage efficiency – the proportion of individuals detected at the entrance of a fishway that successfully ascended the fishways – and ascent rates, and conclude that both vertical slot fishway designs effectively facilitate the passage of pouched lamprey and likely other lamprey species.