We found the lifeguards at the Family Beach to be very vigilant. In the afternoon, an eel was in the snorkeling area, and everyone had to get out of the water until it left. I don't know if all eels are dangerous, but I guess they err on the side of caution.
Also, in the snorkeling area, early in the day, my daughter and I did see a huge round jellyfish just sitting on the bottom, about 12 feet down or so (I am bad at judging distance, but it sure seemed really far down). It wasn't moving, and I am not sure if they remove people due to jellyfish presence. We didn't tell anyone because at the time, we had no idea that they watched for anything but sharks!