The largest towns on its banks are Huaquillas, in the Ecuadorian province of El Oro, and Aguas Verdes in the Tumbes Region of Peru; both towns are connected by an international bridge. The water flows through a canal as the river passes these populated areas. Pollution is a problem in this part of the river, as people from both countries discharge their waste into the canal.
In 1998, during El Niño, the river changed its course, moving 1 square kilometre of land into its eastern margin. Ecuadorians took advantage of this situation, saying that the river is the natural border marker and therefore gives them rights in the affected area. The Peruvians argued that the area is sovereign Peruvian soil.
View of Zarumilla River from international bridge linking Ecuador and Peru in Huaquillas.