Id avoid doing this with a nice bike. Find a beater. Remember, it doesn't really matter how strong it is, your landing in water. Geo isn't a huge deal, you don't need to stick landings. As long as it's flickable, your good. Use like an old P. bike, or an ancient Sasquatch or some thing. A Specialized Hardrock would be really light, handle a similar to a djer, and dirt cheap as well. Lake jumping is so much fun, do whatever you can to make it possible!
That's like saying "I'm going rally racing in my Lamborghini Gallardo. Will that mess up my suspension and tires?" LOL, of course the answer is YES. Sealed bearings are not completely water-proof.
salt water will f*ck it up no end but fresh water should be fine as long as you dry it all off and regrease it afterwards. and threading an inner tube through the spokes of each wheel and then pumping the tube up is the easiest way to keep it afloat i guess.