Iwahig River

The Iwahig River, also known as Balsahan River, is a watershed located in the Iwahig Penal Colony in Palawan, Philippines. It has an elevation of 8 m with an approximate length of 4.14 km The river basin is a 22,859 ha watershed encompassing the city of Puerto Princesa in Palawan province.

Topography
The basin area has a gentle a slope to steep slopes with an elevation range of 10 m to more than 300 m above sea level. Soil types includes Guimbalaon clay, Taburos clay and Bay clay loam. The basin's large area are unclassified with its mountainous land with a closed canopy of trees that covers almost the entire basin.

Flooding
The towns of Iwahig ang Montible were found susceptible to flooding by the study conducted by the Mines and Geosciences Bureau.