Puerto Rico lies at the boundary between the Caribbean and North American plates. This means that it is currently being deformed by the tectonic stresses caused by the interaction of these plates.
Deep oceans waters fringe Puerto Rico. To the west, the Mona Passage, which separates the island from Hispaniola to the west, is about 80 miles (130 km) wide and more then 3,300 feet (1,000 meters) deep. Off the northern coast in the Atlantic Ocean at the boundary between the Caribbean and North American plates is the Puerto Rico Trench, the largest and deepest trench in the Atlantic. The trench is 800 kilometers (497 mi) long and has a maximum depth of 8,000 meters (26,247 ft) at Milwaukee Deep, which is the deepest point in the Atlantic Ocean. To the south the sea bottom descends to the 16,400 feet (5,000 meters) deep Venezuelan Basin of the Caribbean.
Puerto Rico, due to its relatively short width and its east-west running mountain chain, does not have long rivers or large lakes. The longest river is the Grande de Arecibo, which flows to the northern coast. Other rivers include La Plata, Cibuco, Loíza, and, Bayamón all draining to the north, and the Grande de Añasco, draining to the west. There are other perennial rivers, mostly draining to the north and west. Many of the rivers draining south run dry most of the year; nonetheless, with heavy rainfall, they can cause flooding.
Puerto Rico does not have natural lakes, although it has 15 reservoirs, commonly called lakes, formed by damming the main rivers to produce hydroelectric power and water for irrigation. Hydroelectricity accounts for less than 1% of the electricity generated, as most electric power uses petroleum as the