|Ilagan River (Pinacauan De Ilagan)|
|Source||Ilagan River source|
|- location||Sierra Madre Mountains, Casiguran, Aurora, Central Luzon|
|- location||Ilagan, Isabela|
|Basin||3,132 km2 (1,209.27 sq mi)|
|- average||9,455 m3/s (333,900.17 cu ft/s) |
Ilagan River is a river in the province of Isabela, Cagayan Valley, Philippines. It is one of the major tributaries of the Cagayan River, the largest river in the Philippines. The Ilagan River originates from the western slopes of the Sierra Madre and drains the eastern central portion of the Cagayan River basin. It has an estimated catchment basin size of 3,132 square kilometers  and an estimated annual discharge of 9,455 million cubic meters. It flows westward and joins the Cagayan River at Ilagan City, Isabela.
Major tributaries of Ilagan River are:
- Abuan River-Originated from the mountains in the Northern Sierra Madre National Park where one of the widest tropical rainforest in the Luzon can be found.
- Bintacan River
- "The Cagayan River Basin". ABS-CBNNews.com. Retrieved 20 March 2014.
- Riverine Zone Development Framework Plan 2005_2030.pdf "Cagayan Riverine Zone Development Framework Plan". National Economic and Development Authority-Regional Development Council Region 2. Retrieved 20 March 2014.
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