The Agusan River is third longest river in the Philippines, located in the north-eastern part of Mindanao island, draining majority of the Caraga region and some parts of Davao de Oro. It is the country's third largest river (after the Cagayan River and Rio Grande de Mindanao) with a total drainage area of and an estimated length of from its origin. Geography The headwaters of the river are found in the mountains of Davao de Oro, near its border with Davao Oriental and east of Tagum. It flows through the wide Agusan River valley which measures from south to north and varies from in width. It finally drains into the Butuan Bay at its mouth in Butuan. One of the prominent features in the Agusan River basin is the presence of the Agusan Marsh covering a total area of . The marsh serves a flood retention basin for the Agusan River, cutting the high discharge of water causing flash floods in the lower reaches of the river. Aside from that, the marsh harbors unique and pristine habitats like the sago and peat swamps forest and is a home to endangered and endemic flora and fauna. As a consequence, it was designated a wildlife sanctuary by then-President Fidel V. Ramos in 1996. Watershed The Agusan River basin is divided into three sub-basins on the basis of topographic features: the upper Agusan River basin, the middle Agusan River basin, and the lower Agusan River basin. The upper Agusan River basin is the section from its headwaters in the mountains of Davao de Oro to Santa Josefa, Agusan del Sur to Veruela, Agusan del Sur, the middle Agusan River basin is the section of the river from Santa Josefa to Amparo, Agusan del Sur while the lower Agusan River basin is from Amparo to its mouth at Butuan. See also List of rivers of the Philippines References External links Rivers of the Philippines Landforms of Agusan del Norte Landforms of Agusan del Sur Landforms of Davao de Oro Butuan