The Urauchi River is the longest river in Okinawa Prefecture, and it is found on Iriomote Island, the largest of the Yaeyama Islands.As Okinawa consists of many small islands, its perhaps not surprising that the longest river is only just over 18km in length.the river source is in the middle of the mostly uninhabited island at 311 meters elevation and reaches the sea at the NW of the island.Boat