[Al Skierkiewicz]

John and Allan,
This will bring into play a new set of problems. There are a variety of waterproof and water resistant mics available. You are going to have to search. The military has been using mics that can be used in all kinds of harsh environments. Mil surplus dealers may have some in stock that you can pick up cheap. The kind of code that you describe (three letter groups at five words per minute, machine generated) will lend itself fairly well to the techniques that Alan described above with a caveat. The pool environment will likely give some fairly strong reflections of the original signal and a variety of other sounds as well. This will require some filtering so that the morse decoder will not be fooled. Since it is a repeating code, it shouldn't be too difficult. Good luck.