Local knowledge of people using floodplain fisheries can play an important role in informing the management of fish passages and fisheries resources. This paper describes local people’s knowledge of Mekong fish species including where they are caught and perceptions of fish movements in and out of the Pak Peung wetland in Lao PDR. Semi-structured interviews were conducted in 2011 with 81 households from six villages around the wetland. The survey was repeated in 2015 to ascertain any changes in practices and observations of fish migrating up a fish passage, one year after becoming operational. Respondents mentioned 55 fish species in the wetland and showed the most likely locations where they were caught. Women caught a broader range of species than men but less quantity of fish Respondents also identified species they use for fresh consumption, processing and for sale. Prices received for fish varied according to species. The majority of respondents observed that fish numbers had declined in the last 20 years for most species. The most obvious decreases had been in populations of Pa Dook, Pa Etie, Pa Kar, Pa Kilam, Pa Kor, Pa Kot, Pa Kupkong and Pa Park. Reasons for the decline were thought to be due to more people fishing using modern methods, habitat destruction, fishing at the regulator, fishing during the breeding season, not enough water in the dry season and lack of an active management plan for the wetland. However, several households reported catching fish species not seen in the wetland for many years post fish passage including two endangered species and one vulnerable species. Local knowledge of fisheries is important as a complement to scientific measurements to inform best practice management of fish passages and floodplain resources.