Río Pastillo is a river in the municipality of Ponce, Puerto Rico. It is also known as Río Marueño in the area of the municipality where it runs through barrio Marueño. Together with Cañas River, Pastillo forms Matilde River. Pastillo is one of the 14 rivers in the municipality. The river originates at an altitude of 435 feet. Its tributaries are Quebrada Limon and Quebrada del Agua brooks and the river runs for 19 kilometers before feeding into Río Matilde at a height of 15 feet in Barrio Canas Urbano.
Río Pastillo has its origin in the northern mountains of Ponce's Barrio Marueño, in an area called Yagrumo. This river runs for approximately before reaching barrio Canas in the city of Ponce where it merges with Río Canas to form Matilde River. The Government of Puerto Rico has plans to canalize this river.
Quebrada Limón and Quebrada del Agua are two of the main feeder streams to Pastillo River. Quebrada del Agua was diverted via canali