Seasonal floodplains under private and public ownership in the Indo-Ganges river basin provide food and income for millions of people in Bangladesh. This research aimed to understand the complex institutional relations that govern ownership, access, and control of the floodplains under Community Based Fish Culture (CBFC) to increase fish production and overall livelihoods of the poor. Stakeholders representing various institutions and organizations, like the Department of Fisheries, the Land Department, and Floodplain Management Committees, as well as the lease holders of public water bodies in the floodplains, private landowners, seasonal and professional fishers were interviewed. The willingness of people from different social classes to work together, the adoption of new technology, the benefits of cooperation, and the embeddedness of local institutions are shown to be important inputs for policy making. The research also shows that existing co-management arrangements characterized by unequal power distribution among the different actors often resulting in the marginalization of the professional fishers and the landless poor fishers. The CBFC model introduced by WorldFish and Bangladesh government institutions attempted to reach a more equal representation of stakeholders, improved distribution of power, conflict resolution, and a mechanism of accountability in the decision making on fish culture activities in the public and privately owned floodplains of Bangladesh. The intervention in seasonal floodplains positively impacted fish production, consumption, and incomes. Also, food security of the participating households has improved, and CBFC had a positive and significant impact on fisher’s expenditure, showing an equalization effect on expenditure for food, clothing, and health. Furthermore, the CBFC management system helps to more equally distribute total expenditure among the fisher communities. Indirect benefits of Community Based Fish Culture include improved social capital, greater cooperation, and reduced conflict in the floodplain community.