Ha, I'm not surprised they failed mention the sharks before taking you on to the water. Here are some links:

http://www.ibtimes.com/articles/200227/20110818/shark-attack...

http://www.tripadvisor.com/ShowTopic-g147326-i649-k4748070-S...

Having said that, I would swim again in that water without concern - thousands of tourists did it before and after me, what happened to that woman was just bad luck.