So after a bit of detective work on the web it looks like San Fran Bay had a water temperature of 48 and 49 degrees at 7am on May 2, 2009 and 2008, respectively. Comparatively, the water was 59 degrees at 7am on June 14, 2009 (last race date).
The race website notes that the average water temperature is 55 (which feels significantly colder than ~59). Sub-50 degree temperatures are a pretty scary proposition. What, if anything, can we do to prepare for a sub-50 temperature race?
Sign up for the TriCalifornia event in August?
swim faster? HTFU? Don’t sign up for that race? Get a water rover?
On the other hand the way RD’s bail on the swim at the sight of a 1ft wave, if it’s that cold I bet they shorten it or cancel the swim.
There are also the Great White Sharks that roam the SF bay
http://www.mercurynews.com/top-stories/ci_13705787?nclick_check=1
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I raced World’s Toughest Half in 2004 (I think it was 04). Water temp was announced at 49F. I made it out. Heck, I even finished the race! So, you should be able to survive 
Looks like you need to get the Desoto water rover wetsuit. :o)
Dave
I raced World’s Toughest Half in 2004 (I think it was 04). Water temp was announced at 49F. I made it out. Heck, I even finished the race! So, you should be able to survive
Yes, it was 2004. I was just looking at the photos from that last night.
clm
Three words: Sounds. Like. Fun.
What’s the word on why they moved the date?
Pedro Ordenes used to (might still) lead the training group at aquatic park in SF.
He swam the Strait of Magellan in 39 degree waters.
http://www.youtube.com/watch?v=aqhB0SWI7lE
To train, he use to spend long periods in a bathtub full of ice water. If you spend enough time in a tub full of ice, the 48 degree water should feel pretty warm. 
I have a feeling that measurement (48-49) was taken from a buoy out in the open ocean, not anywhere in the Bay. The Bay is always warmer.
I swim in the Bay year-round, including some spring and fall crossings from Alcatraz. The water can dip below 50 degrees in Jan-March, but by early May is always back up above 56 degrees. I think the likely range you can expect on May 2 is more like 56-60.
Additionally, note that the Escape from Alcatraz swims are scheduled during ebb tides. Ebb tides are usually warmer than flood tides. So, if the average temp in the Bay that day is 58, it might be 57 during the flood tide and 59 during the ebb tide when the race is happening.
The real thing I would worry about in early May is that the tides and currents can be a bit more unpredictable or volatile than in early June. There are more springtime patterns: Unexpectedly strong currents; ebb starts an hourly early or an hour later than expected; strong eddies on the shore; etc. It’s nothing dangerous, it’s just that you’re more likely to have to adjust your sighting strategy mid-swim, compared to an easy summer swim from Alcatraz.
I hope that, uh, makes you feel more confident Swimming from Alcatraz is truly a blast.
Three words: Sounds. Like. Fun.
What’s the word on why they moved the date?
That’s a very good question. Interesting that it ended up the same weekend as Wildflower, Napa 1/2, The Relay and Wine Country Century.
clm
I raced World’s Toughest Half in 2004 (I think it was 04). Water temp was announced at 49F. //
I did it that year too, and folks should note that was fresh water, which is much colder than the salt water in SF bay at the same temp. That was some butt cold ass water for sure, only one swim I ever did that was worse. That was China the first year we were there, 48 degree river water…But for the non wetsuit swims, it was Puegot sound in Washington, 51 degrees for the USTS race there in 83. Needless to say they did not cancel the swim, but did cancel the race the next year…
No problem for the Canucks coming down. This is how we train all winter
For once I actually had a decent swim…I guess the cold water forced me to push…Now I was so cold after it took me literally 10min to get out of my wetsuit (I sat next to that thing in T1, blowing hot air, and no it wasn’t big kahuna 
-hope you’re reading this)
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I raced World’s Toughest Half in 2004 (I think it was 04). Water temp was announced at 49F. //
I did it that year too, and folks should note that was fresh water, which is much colder than the salt water in SF bay at the same temp. That was some butt cold ass water for sure, only one swim I ever did that was worse. That was China the first year we were there, 48 degree river water…But for the non wetsuit swims, it was Puegot sound in Washington, 51 degrees for the USTS race there in 83. Needless to say they did not cancel the swim, but did cancel the race the next year…
Don’t be offended, but this is simply wrong. What determines how cold water feels is the water temperature, how much of your body is submersed in water, the presence of any wind, the air temperature and finally the effectiveness of any wetsuit you may be wearing. While there is a density differential, it’s impact is insignificant when compared to other factors.
Don’t be offended, but this is simply wrong. \
I’m not offended, most people are like you and think that salt and freshwater temps are the same…The actual tempeture on the thermoter may say the same number, but they are wildly different in how they affect your body…I know that it sounds counter to what everyone thinks, isn’t 79 degrees 79, no matter what the medium???
If you want to do your own test, you most likley already have, but just never put it together…GO to a 75 degree ocean like hawaii or florida…Go for a swim sans wetsuit and see how you feel…Now go to a freshwater lake, or your local pool even, ans swim in it at 75 degrees…You may have been in the pool when the heater broke, and if it got to be 75 or lower, you should remember how frigging cold it was… Remember a 70+ degree ocean and how it felt??? Like bathwater, but both the same on the temp guage…It is a function of how much salt in in the water, it has an insulating property to the human body…SO if you want to argue that the actual temps are the same, I agree. WHat I do not agree with is the impact each has on us as swimmers, and after all, that is what really matters…
Don’t be offended, but this is simply wrong. \
I’m not offended, most people are like you and think that salt and freshwater temps are the same…The actual tempeture on the thermoter may say the same number, but they are wildly different in how they affect your body…I know that it sounds counter to what everyone thinks, isn’t 79 degrees 79, no matter what the medium???
If you want to do your own test, you most likley already have, but just never put it together…GO to a 75 degree ocean like hawaii or florida…Go for a swim sans wetsuit and see how you feel…Now go to a freshwater lake, or your local pool even, ans swim in it at 75 degrees…You may have been in the pool when the heater broke, and if it got to be 75 or lower, you should remember how frigging cold it was… Remember a 70+ degree ocean and how it felt??? Like bathwater, but both the same on the temp guage…It is a function of how much salt in in the water, it has an insulating property to the human body…SO if you want to argue that the actual temps are the same, I agree. WHat I do not agree with is the impact each has on us as swimmers, and after all, that is what really matters…
I’d like to see some science on that.
As for how you feel in salt water verses fresh water, that is psychological not physiological. Try swimming in an ocean and a lake without a wetsuit for an hour at 75 degrees. I can assure you that you’ll feel the same at the end. Your initial impresion of the temperature could simply be the difference in air temperature or stregth of sun on your skin. It also could be a response to your expectations.
Something happens to water when you add salt to it…It does not freeze at the same temp as fresh water, so unless that is an illusion also, then something is different at the same temps… I assure you it is not the sun, it is not a placebo affect, or something just made up…As you asked, I have swam in oceans and lakes for miles and miles, and it is not the same on the human body…Have you ever done the swims I talked about??? Been to Hawaii where it is 75 degrees, and you can stay out and just play all day?? See how long that playing lasts in a 75 degree pool…They are absolutly different, and it is all about the salt…
This past year I did a 4K lake swim. There was no seperate a wetsuit division so I wore one and had to open it to let in cool water. I also swam nude in a 5K ocean swim with a heavy current, Alcatraz to Aquatic Park, and Aquatic Park to Alcatraz and back to Aquatic Park. I also did 2 triathlons with pool swims, 2 with lake swims (one I swam without a wetsuit), one with a river swim and one with an ocean swim. I also get to Hawaii nearly every year.
As far density, salt water is denser and if anything it would conduct heat away from your body quicker. Salt in water changes the boiling and frezing point but that would have no effect on you unless you are swimming in 0 C or 100 C water. Keep in mind that there are quite a few pools that use a salt system as well.
those races are great for novelty but the sure don’t seem fun to me.