River development in Lao P.D.R. has led to construction of numerous water regulation devices (over 10,000) which limit migratory fish movement. Movements of fish (and other aquatic animals) between rivers and floodplains is subsequently restricted, or may be entirely prevented, and this has led to severe declines in fish production in many areas. Fish-passage technology has the potential to enable movement of migratory fish past these low-level (less than 6 m) barriers. Consequently, fisheries agencies are interested in increasing capacity to design, manage and operate fish passage facilities on new and existing low-level water control structures. The first fishway in Lao P.D.R. was constructed and assessed at a wetland regulator between 2011 and 2014. Over 170 species, from a range of size classes, were captured within the fishway. Many species successfully recolonised a wetland which had been previously disconnected by regulator construction. But not all species were able to ascend, and local hydrology substantially impacted fishway effectiveness. These observations suggests that fishways may be an important tool for increasing fisheries productivity in the Lower Mekong Basin. But capturing a high number of migratory species, with a range of different swimming abilities, indicates that strategies to suit all fish will require diverse and flexible solutions.