Agusan River is a river located in the eastern part of Mindanao island in the Philippines, draining majority of the Caraga Region and some parts of Compostela Valley province. It is the third largest river basin of the Philippines with a total drainage area of 10,921 km² and an estimated length of 350 kilometers from its origin. The headwaters of the river is found in the mountains of Compostela Valley, near its border with Davao Oriental and east of Tagum City. It flows through the wide Agusan River valley which measures from south to north and varies from 32-48 kilometers (20–30 miles) in width. It finally drains into the Butuan Bay at its mouth in Butuan City. The river is also the third longest river in the Philippines.