Vieques (vyā´kās), island (1990 pop. 8,602), 51 sq mi (132 sq km), off E Puerto Rico. It is hilly, with a dry, warm climate. The town of Vieques, commonly called Isabel Segunda, was founded in 1843 and is the main population center. The island has gained popularity as a resort. Mosquito Bay, also known as Bioluminescent Bay, S central Vieques, is noted for the bioluminescence of the dinoflagellates (see Dinoflagellata) that live in the bay.
Most of Vieques was within U.S. military installations from the 1940s. The facilities included a live-ammunition training area for the U.S. navy, a use that was the subject of protests by many Puerto Ricans. In 2001 the federal government announced that it would halt all military exercises on the island by May, 2003, but in the meantime use of the island for training continued to spark protests. The former installations are now being converted to a wildlife refuge and cleared of unexploded munitions.