The reserve is one of six protected areas located in the Agno River Basin, the third largest river system in Luzon and the Philippines' fifth largest. It is a sub-catchment of the Agno River which drains into the Lingayen Gulf from its headwaters at Mount Data further north. Its main tributary within the reservation is Twin River at its northern portion which has its source in the peaks around Baguio and which splits into several streams in the Gumatdang mining village, including the Ambalanga River, Liang Creek and Batuang Creek. The central and southern sections of the reserve are fed by other branches of the Agno River, namely the Laboy and Ambayoan rivers as well as several streams in the Padcal mining area of Ampucao and Dalupirip villages including Balog River, Albian Creek, Manaa and Salangan Creek.