Bridging the Mekong: The first basin-scale fish passage inventory

The Mekong River Basin (MRB) supports the world's most productive inland fishery, but is becoming increasingly fragmented by river infrastructure, with more than 13,000 barriers already present and further expansion expected. Fish passage facilities (FPFs), such as fishways, offer a potential mechanism to mitigate connectivity loss, yet their distribution and characteristics across the basin have not previously been synthesised. Here, we present the first basin-scale dataset of FPFs in the MRB, the MRB FPF Inventory, to support environmental authorities in planning fish passage investments. We identified 80 FPFs constructed or proposed since 1994, representing only 0.6% of known barriers. These measures were dominated by fishways (65.0%), with most intended to restore longitudinal connectivity (71.3%) and support bidirectional passage (77.5%), and were concentrated primarily at irrigation weirs (68.8%) and large hydropower dams (17.5%). Implementation has accelerated in recent years, with 58% of FPFs constructed or proposed since 2020, although their distribution varies markedly among countries and infrastructure sectors. Notably, only a small proportion of FPFs have been evaluated, indicating that the effectiveness of fish passage restoration across the basin remains largely unquantified. The MRB FPF Inventory provides a baseline for prioritising future investments and highlights the need for coordinated, basin-scale strategies to restore migratory connectivity in one of the world's most important inland fisheries.