Abstract. The Giam Siak Kecil -Bukit Batu (GSKBB) Biosphere Reserve in Riau Province has flood swamp forest ecosystem, which is served as the primary fisheries resource for the local community. This research is aimed to determine the characteristics of resources and fishing communities, as well as the local institution in utilizing of water resources using Ostrom's principles (1990). This research uses qualitative methods. The data are collected and validated through three techniques which are in-depth interviews, participant observation, and documents study. Analysis was conducted by descriptive-qualitative. The results show that most of fishing communities were Siak Malay ethnic, who still used traditional fishing gear. Water resources of GSKBB are classified as Common Pool Resources (CPRs), which make it difficult to cope for free riders. Fishing communities have local institutions, namely: the boundary of technology, property rights, supervision, social sanctions, and the conflict resolution mechanism. There are no boundary of time and fishing in the area because fishermen wisely adapted to a natural condition such as water fluctuations in water level of rivers and lakes. There are also no limitation of users and the number of unit resources that should be applied because fish resources are still abundant.