The Puerto Princesa Subterranean River National Park (PPSRNP) is one of the most important biodiversity conservation areas of the Philippines. It features a spectacular limestone or karst landscape that contains an 8.2 km long underground river. A distinguishing feature of the river is that it flows directly into the sea, and the lower half portion of the river is brackish and subject to tidal influence. The area also represents significant habitat for biodiversity conservation. It contains a full mountain to the sea ecosystem and protects forests, which are among the most significant in Asia.

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