|Depends how much you are prepared to spend. If you send the drive to a specialised data recovery company they may be able to recover the data. They will open the disk in clean-room conditions, take out the platters and put them in a new case and hopefully be able to recover some data.|
The chlorine in the pool will have destroyed the electronic but the platter is in a sealed case so they may be usable. Be prepared to pay a four figure sum.
Next time keep more than one copy of your data, three is normal. It is just asking for trouble to stake your livelihood on a piece of rusty aluminium which is all a hard disk is.