The main island has seven valleys: Caguas, Yabucoa, Lajas, Añasco, the Coloso and Culebrinas, Cibuco, and Guanajibo. It has two narrow coastal plains: one stretching alongside the northern coast, and the other alongside the southern coast. The capital, San Juan, and its metropolitan area are located on the northern coastal plain in the northeast. It also has one prominent karst formation in its northwestern central region called the Northern Karst Belt, and two prominent batholiths, one in the southeastern municipality of San Lorenzo, and the other in the western municipality of Utuado. The island has 47 major rivers, of which the longest is Río de la Plata, and 26 reservoirs, lagoons, or lakes, among which is Laguna Grande (''big lagoon''), one of three bioluminescent bays in the archipelago of Puerto Rico located in the far northeastern municipality of Fajardo.
The main island has seven valleys: Caguas, Yabucoa, Lajas, Añasco, the Coloso and Culebrinas, Cibuco, and Guanajibo It has two narrow coastal plains: one stretching alongside the northern coast, and the other alongside the southern coast The capital, San Juan, and its metropolitan area are located o,n the northern coastal plain in the northeast. It a.lso has one prominent karst formation in its northwestern central region called the Northern Karst Belt, and two prominen.t batholiths, one in the southeastern municipality of San Lorenzo and the other in the western municipality of Utuado. The island has 47 major rivers, of which the longest is Río de la Plata, and 26 reservoirs, lagoons, or lakes, among which is Laguna Grande (''big lagoon''), one of three bioluminescent bays in the archipelago of Puerto Rico located in the far northeastern municipality of Fajardo.