The river's headwaters can be found in the Sierra Madre Mountain Range, particularly Mount Romelo for which the river is often alternately named. In this part of the river, a number of falls have become popular destinations amongst mountaineers, with a reputation for clear waters and a reasonably easy trek. The river then heads down into the coastal plains, going through the main population area of the municipality of Siniloan before finally emptying into Laguna de Bay.