If it's fresh water I'd still have hope for her, I'd be ducking a diving and feeling in the blind at the bottom for hours until I found her. Keep the faith. If you do find her make sure you wash her out for 15 to 20 mins, ideally I think it's deionised water that the experts recommend but I threw mine into a big sink of tap water, opened her up, let the tap run through everything left her submerged in the clean water for 20 mins ( it feels completely unnatural and wrong but do it) dry her out as much as possible, hairdryer but air compressor is best and then into a big blastocyst bag full of rice for a few days tied at the top. Don't be tempted to try power it up too soon just leave her in the rice for 5 days (maybe too long but that's what I did) just forget about her and then cross everything when you open it back up. Make sure every grain of rice is out especially from the esc's as they tend to lodge in there, don't use anything sharp to remove rice from them just shake, jiggle or use an air compressor to try and dislodge any stubborn grains of rice left. Then all you can do is try per her up. As I said mine worked flawlessly after her salty seawater bath but if not you will only have to replace a few bits and pieces, the battery will hopefully be your biggest loss.