The country's most extensive river systems are the Pulangi (Rio Grande), which flows into the Mindanao River; the Agusan, in Mindanao which flows north into the Mindanao Sea; the Cagayan in northern Luzon; and the Pampanga, which flows south from eastCentral Luzon into Manila Bay. Laguna de Bay, southeast of Manila Bay, is the largest freshwater lake in the Philippines. Several rivers have been harnessed for hydroelectric power.