The twin-engine Piper Geronimo was heading to St. Thomas, US Virgin Islands, when an engine failed shortly after takeoff from San Juan, said Maria del Pilar Bon, a police spokeswoman.
The plane crashed into the Condado Lagoon, a shallow inlet surrounded by high-rise hotels and apartments in the upscale Condado tourist district.
Many people witnessed Monday's crash and paddle-boarders and kayakers rushed over to provide assistance. The pilot, 40-year-old Rafael Augusto Pesquera and the passenger, Ramon Garriga Ortiz, 49, scrambled out as the aircraft quickly sank. Neither had any injuries, said Oscar Sotomayor, operations director for Puerto Rico's Emergency Management Agency.