In northern Iriomote, Urauchi River is Okinawa's longest (19 km), widest (200 m), and deepest (15 m) river. It's home to a whopping 400 species of fish or 10 percent of Japan's fish species.

Over 20 fish species are endangered. Urauchi River is within Iriomote-Ishigaki National Park. Both sides of the river are lush with mangroves and forests. 西表国立公園