The two began looking around in the very clear water for the mysterious guest and saw nothing. As they moved around in this search, the two were a few feet apart with their backs relatively toward each other, and were approximately fifteen or twenty feet from shore, when Maite spotted a large fish swimming immediately past her.
As she was about to say something to her husband, Maite was trying to get the words out to tell Woody about the large fish, but instead exclaimed in "ahh, ahhs." Woody turned around to find out what his wife was trying to say, and noticed the large fish as it had just swam past Maite and was now gliding through the water five feet away in a circular pattern around the two. He simply and slowly spun around watching as he calmly said, "Yeah, that's a shark."
Like a ball shot from a cannon, Maite splashed her way to the tiny beach area and Woody watched as the shark started to circle back before swimming back out to sea, likely started by the stampede that went on a few feet away.
It was only later at home that the married couple realized the gravity of such an encounter. Through a few simple searches, it was determined by both that, without a doubt, Maite had been bumped and circled by a four-foot bull shark, one of the most deadly in the ocean.
The shark was similar to the one below in both size (maybe a bit smaller) and color:

For more information about the bull shark, check out this article: http://www.slate.com/id/112116/
Thank God that the water was freezing and that neither of the couple actually went swimming, as the flailing of arms could have easily been mistaken for fish. You see, before the shark encounter, the two were standing in the water and sporadically saw fish jumping out of the water (likely avoiding the jaws of the 'large fish'). In addition, there were pelicans and other birds feeding a short distance away at the end of a pier. This feeding frenzy was likely what had attracted the bull shark to check out which other goodies were in the area.