Answer:

The Philippines has 412 principal river basins in 119 proclaimed watersheds.

The country's longest river is the Cagayan River, with a length of 505 kilometres (314 mi), followed by the Mindanao River and Agusan River, with respective lengths of 373 kilometres (232 mi) and 349 kilometres (217 mi).[1] With an area of 27,753 square kilometres (10,715 sq mi), the Cagayan River has the largest drainage basin, followed by the Mindanao (23,169 km2 or 8,946 sq mi), Agusan (11,937 km2 or 4,609 sq mi), and Pampanga Rivers (10,434 km2 or 4,029 sq mi).[2]