Agusan Marsh Wildlife Sanctuary is near Bunawan in the interior of north-eastern Mindanao, in the Agusan River Basin, Agusan del Sur. Agusan Marsh Wildlife Sanctuary, protected by law, covers an area of 14,835.989 hectares. The area was given Ramsar site status in 1999. It is a vast complex of freshwater marshes and watercourses with numerous small shallow lakes and ponds in the upper basin of the Agusan River and its tributaries which rise in the hills of eastern Mindanao. Some parts of the marsh are used for traditional fish ponds and rice paddies. The site acts as storage for rain water and reduces the immediate downstream flow of flood water into Butuan City.

Agusan Marsh is one of the largest and the most contained freshwater catch basin wetland in the Philippines. The main habitats of the marsh include freshwater swamp forest ( 49% ), secondary scrub ( 14% ), herbaceous swamp ( 7% ), lakes, pools and rivers ( 10% ), rice paddies and other agricultural land ( 6% ), and small settlements ( 6% ). The Marsh is a valuable habitat for water birds such as species of wild ducks, herons and egrets. It is also the refuge of the rare Oriental Darter ( Anhinga melanogaster ) and Purple Swamp Hen ( Porphyrio porphyrio ) and the threatened Philippine Hawk Eagle, Spotted Imperial Pigeon and Rufous lored Kingfisher.

The National Economic and Development Authority (NEDA) Region XII Ligawasan Marsh Development Master Plan (1999-2025) recommends that it should be accorded immediate protection and conservation prior to any development planning and intervention. The Protected Area Suitability Assessment (PASA) was undertaken by the Philippine Government, as the answer and called for in that plan that is to protect and conserve the rich natural resources and secure the biodiversity of Ligawasan Marsh. The PASA started last March 2001 and ended on March 2002 conducted by Winrock International with the consortium of local Non-Government Organizations such as the MINSUPALA Foundation, Inc. and the Maguindanaon Development Foundation, Inc. with the facilitation and guidance of regional offices of DENR and ARMM. The approach is simple, convergence of major efforts of multi sectoral stakeholders in order to sustain and maintain the Ligawasan Marsh biodiversity and be socially acceptable by the local communities.

Ligawasan Marsh is the largest swamp and marsh area in Mindanao and one of the largest in the Philippines. With an estimated area of 288,000 hectares, of this 43,900 hectares was declared as Game Refuge and Bird Sanctuary. It encompasses three provinces ( Maguindanao, North Cotabato and Sultan Kudarat ) and straddles to three regions, and is a conglomeration of three marshes namely: Libungan, Ebpanan and Ligawasan proper. It covers twenty municipalities, and one city with a total population of 1,094,170 ( Census 2000 ) who are predominantly Maguindanaon Muslims, they called themselves, before the advent of Islam and Christianity, as the " people of the flooded plains ". Ligawasan Marsh is identified as rural in nature, limited access to social services has often attributed mainly to peace and order problem.

The Ligawasan Marsh is also identified as a distinct and unique region among the 15 Bio Geographic regions in the Philippines much bigger than the Agusan Marsh in Northern Mindanao, Philippines