From the 106W website: "The average water temperatures will range from 61 to 64 degrees Fahrenheit". 61F is cold but do-able. 44F is not, especially for thin athletes.

The lady at the marina's response to the claim of 61-64F was "no way".

Alcatraz is what, mid 50s? With how many cases of hypothermia (or worse)?

Edited to answer my own question:
In all, rescuers pulled about 150 swimmers from the swim portion of the race, more than three times the normal number, Burke said. Water temperatures were about 51 degrees, air temperatures hovered in the mid-50s and 11-mph winds made the air feel closer to the mid-40s.
Normally, when the race is held in June, the bay is anywhere from 54 to 60 degrees, and air temperatures can be in the 70s or higher.