It had seemed impossible to escape from Alcatraz by swimming. The seasonal water temperature in the Bay is about 53 °F (12 °C) in December and the current can exceed 6 knots. Citing these facts, as well as occasional visits from Great White Sharks and razor-sharp rocks, prison officers had discouraged most escape attempts. When Frank Morris and brothers John and Clarence Anglin had escaped and disappeared half a year earlier, prison officials had said that they had likely drowned (although the FBI just listed them as missing). Scott's escape shook this line of reasoning. For the first time it was proved that a prisoner could escape (if only temporarily) by swimming.