Cagayan River, also called Río Grande De Cagayan, longest stream in Luzon, Philippines. It begins its 220-mile (350-kilometre) course in a twisting pattern in the Sierra Madre in northeastern Luzon. It then flows north into a 50-mile- (80-kilometre-) wide fertile valley that is important for the cultivation of rice and tobacco. Ilagan, Isabela, Tuguegarao, and Cagayan are major riverine towns. At Aparri, the Cagayan enters the ocean at Babuyan Channel of the Luzon Strait. The Chico, Magat, and Ilagan rivers are its main tributaries.Aparri, town, northeastern Luzon, Philippines. It lies along the Babuyan Channel of the Philippine Sea, near the mouth of the Cagayan River. Aparri is the interisland port for much of northeastern Luzon. Anti-Spanish insurgents landed there in 1898 under Colonel Daniel Tirona, and civil government was restored in 1901 under the United States. The town’s principal exports are rice, corn (maize), copra, logs, and fish products. Fishing, cattle raising, and the manufacture of fish paste are the main local industries. The population is mainly Christian Ilocanos and Ibanags. Pop. (2000) 59,046; (2010) 61,199.