The Rio Grande de Mindanao, also known as the Mindanao River, is the second largest river system in the Philippines, after the Cagayan River of Luzon. It is the largest river on the southern island of Mindanao with a drainage area of 23,169 km2 (8,946 sq mi) draining majority of the central and eastern portion of the island. It is also the second longest river in the country with a length of approximately 373 km (232 mi). It is an important transportation artery on the island, used mainly in transporting agricultural products and, formerly, timber. from wikipedia.