Alcatraz is 3 miles from San Fran according to Google maps.
Not that far - the swimming leg of the current "Escape from Alcatraz" triathlon
is 1.5 miles. If you were to head straight across the island toward Fisherman's Wharf, it might be a little bit less than a mile.
Stupid Google maps. lol I'll take your word for it as I have no familiarity with the area.