The Río Grande de Añasco is a river in western Puerto Rico.

[1] The river flows through the municipalities of Mayagüez, Añasco, San Sebastián and Las Marías.

[3] In the 1898 Military Notes on Puerto Rico by the U.S. it is written that the "Añasco River is formed by the Lares Mountain ridge.

It rises in the eastern extremity of the mountains called Tetas de Cerro Gordo, flowing first northwest, and then west, through the town of its name and thence to the sea.

"[4] It is spanned by the Puente de Añasco, a bridge listed on the National Register of Historic Places.