In December 2001, the Tonle Sap Biosphere Reserve (TSBR) was established by Royal Decree with three complementary functions:
- a conservation function to contribute to the conservation of biological diversity, landscapes, ecosystem, including genetic resources, plant, fishery and animal species, and to the restoration of the essential character of the environment and habitat of biodiversity;
- a development function to foster sustainable development of ecology, environment, economy, society, and culture;
- a logistic function to provide support for demonstration projects, environmental education and training, research and monitoring of environment related to the local, national and global issues of conservation and sustainable development.
The TSBR established a core zone, a buffer zone and a transition zone. The core zone contains protected sites for conserving biodiversity, monitoring minimally disturbed ecosystems and undertaking non-destructive research and related activities. The three core zones are: Prek Toal (21,342 ha), Boeng Chhmar (14,560 ha) and Stung Sen (14,560 ha).
The core area of a Biosphere Reserve is defined as an area devoted to the conservation of biological resources, of landscapes and of the ecosystem. The Royal Decree by which the TSBR was declared concurs with this characterization and cites biodiversity conservation, monitoring and research as the primary objectives of the core area.