River System

The main river systems in Luzon are the following: (1) the Rio Grande de Cagayan, which drains the Cagayan Valley; (2) the Agno River, which drains the rivers in Nueva Ecija, Pangasinan, and Tarlac; (3) the Abra River, which receives its tributaries from the Cordillera and drains Lepanto, Bontoc, and Abra; and (4) the Pampanga River, which drains the rich valleys of Nueva Ecija, Pampanga, and Bulacan.

The largest river system in the Philippines is Rio Grande de Mindanao. It is fed by the waters of two large lakes and drains the central Mindanao basin. Another principal river in Mindanao is the Agusan, which drains the Surigao basin.

Other famous Philippine rivers are the Pasig River which runs through Manila, the Jaland and Panay Rivers in Panay, and the underground river found in Palawan.