The Magat River is a river in the Philippine island of Luzon with a total length of 226 kilometres (140 mi). It originates in the Nueva Vizcaya municipality of Aritao, where the Santa Fe River joins the Marang. It is the largest tributary of the Cagayan River by discharge volume of water, with an estimated drainage area of 5,200 square kilometres (2,000 sq mi), roughly twenty percent of the total drainage area of the Cagayan River.