High Quality Content by WIKIPEDIA articles! The Río Grande (sometimes called the Río El Yunque) is a river in the U.S. commonwealth of Puerto Rico that flows through the El Yunque National Forest and the town of Río Grande. From this junction the river is given the name Río Caine for 162 km and continues to flow in a southeasterly direction, before it is called Río Grande. After a total of 500 km the river turns northeast and in a wide curve flows round the lowland city of Santa Cruz.