Río Bayagán is a river in the municipality of Ponce, Puerto Rico. Bayagán is a tributary of Cerrillos River. It has a length of approximately six kilometers and runs in a southerly direction, mostly along PR-505. It originates in barrio Montes Llanos and runs south through barrio Machuelo Arriba for about nine kilometers until it meets Río Cerrillos. It is part of the Bucaná River watershed. This river is one of the 14 rivers in the municipality.