| Iwahig River | |
| Name Other: | Balsahan River |
| Pushpin Map: | Palawan#Philippines |
| Pushpin Map Caption: | Iwahig River |
| Subdivision Type1: | Country |
| Subdivision Name1: | Philippines |
| Subdivision Type2: | Region |
| Subdivision Name2: | Palawan |
| Subdivision Type3: | Province |
| Source1 Coordinates: | 9.1497°N 118.0811°W |
| Basin Size: | 22859ha |
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 with an approximate length of The river basin is a 22859ha watershed encompassing the city of Puerto Princesa in Palawan province.
The basin area has a gentle a slope to steep slopes with an elevation range of to more than above sealevel. 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.
The towns of Iwahig ang Montible were found susceptible to flooding by the study conducted by the Mines and Geosciences Bureau.