The floodplain wetlands (beels) constitute important fisheries resources of Assam. These resources are managed through a complex social framework. The state of this management regime determines the level and sustainable utilization with implications on fisheries and livelihoods. To find the impact of such management regime, a case study has been undertaken in the Dhir beel of Assam. The impact of the change in the management regime on the sustainability of fisheries and livelihoods of fishers has been evaluated. This change in the management regime has been due to immigration of a large number of people from the nearby areas since 1985. The study has compared the scenario that existed ‘before 1985’ (data of 1982-84) and “after 1985’ (data of 2004). There has been a significant increase in the fishing pressure with new fishing practices (1.5 to 5 times) as well as intensity of effort (3 to 7 times). The weakening of the regulating institutions has led to irrational practices which in turn, have resulted in a decline (22.32%) in the production and productivity of the beel. The decline has been more (31.79%) in terms of value than production of fish, indicating a definite decline in the quality of the fish available in these resources. In the changed scenario, the economics of the management has gone against the resource managers as they are to spend more money on monitoring and enforcing the rules. The livelihood of the fishers has also declined with the high degree of sharing of fish among the fishers.