Braxton Bilbrey, a second-grader from Glendale, Ariz., made the estimated 1.4-mile swim to Aquatic Park in 47 minutes, according to his coach.
"I think it's pretty cool," the wetsuit-clad boy said shortly after his father grabbed him under the arms and lifted him from the chilly water.
Braxton, who said his next ambition is to swim the English Channel, swam freestyle, his favorite stroke, the whole way.
Accompanied by his coach, Joe Zemaitis, and two other adults, he was greeted at the beach on the sunny, mild morning by reporters, photographers, family members and other well-wishers.
"He did great," said his dad, Steve Bilbrey. "He looked so strong. He did so awesome. I'm so proud of him."
Zemaitis, who has completed the Escape From Alcatraz Triathlon seven times, said the fast crossing was partly due to flat water and good tides. San Francisco Bay is known for its strong currents and rough waters that are usually churned up by winds that roar through the Golden Gate.
Braxton's mother, Stacey Bilbrey, wasn't originally sold on the idea of the swim, but she accepted it once the boy proved his dedication, training two hours a day, four times a week.
"Any time a 7-year-old has that strong of a desire, as long as it's a good desire, you should support it," she said. "He's worked hard for it."
Alcatraz, once a notorious federal prison that housed some of the nation's infamous criminals, including Chicago mobster Al Capone, is now a tourist site that attracts about 1 million visitors a year. It also draws a fair share of swimmers who attempt the crossing as part of the annual triathlon.
The Arizona boy got the idea when he saw a magazine story about a 9-year-old boy who made the swim. Johnny Wilson, a fourth grader from Hillsborough completed the swim in 53-degree waters last October in under two hours.
Zemaitis said Braxton was going to get something to eat and then take it easy.
"He's going to rest up," Zemaitis said. "He's had a big day."