Pulling data from a drowned hard drive?

You may have a chance here!

First have you pulled it out of the system yet? The sooner you do the better your chances.

You'll need to wash it down the external parts of the drive with distilled water to get any mud or other stuff off. Then using isopropyl alcohol wash it down again use a soft brush to scrub any stuff junk or corrosion (be careful not to over scrub as some components could come off). The internal platters & head assembly should be OK. Shake out any moisture then let it air dry at least a few days some where warm.

Now the hard part, you'll need to get an external Firewire or USB case to mount the drive to. Before you power it up make sure you have enough storage on the system for all of the data as you may only get one chance in getting the data off.

If it doesn't start up and the data is that important you'll need to send the drive in to a clean room HD salvage service to recover the data but it will be very costly!