It is supposed to be waterproof to 25 feet, but many report that they leak. This could just be because of improper care of the O ring too. Suggest you read a field test report at
http://lostreasure.com/fieldtests/ArchiveView07.cfm?ID=LT20070625
You might wanna wrap this PI around a tree since it loves to find iron very deep. Bobby pins can last decades in fresh water ut will rust away sooner in salt. If you are young with a strong back it will find the deep stuff. Myself however would rather spend my time with a detector with more discrimination like a Excal that ignores iron and still respond to coins and rings very near or under the iron. It can still respond to a large iron object just like the other detectors.
I prefer the Excal 1000 and the Tiger Shark or CZ20 for all my water hunting.