I work in an oceanographic research lab as an electronics tech, so I have a fair bit of experience salvaging wet electronic gear.
The first thing we tell field crews to do is NOT TO LET THE EQUIPMENT DRY OUT until they get it back into the shop. Once the equipment starts to dry, corrosion sets in immediately, especially in a salt water situation. Remove the batteries immediately, and rinse the equipment with distilled water to remove as much of the dirty water as possible. If it will be a while before you can dissasemble and dry the device, keep it submerged in distilled water.
Although it may seem counterintuitive, water itself is actually not all that damaging to electronics. It is all the stuff DISSOLVED in the water that causes problems. Most electronics are actually washed with water at the factory nowadays.
Once on the bench, standard procedure is to disassemble the device down to individual circuit boards, and wash with a mild solvent like anhydrous IPA to displace the remaining water from all the crevices. Simpler components can then be dried under a heatlamp or hot air blower, while more complex items get placed in a vacuum oven at around 120F for a couple of hours. Certain components need to be removed from boards before being given the vacuum treatment, such as batteries and large electrolytic caps, which can rupture under external vacuum.
Connectors and the like are washed out with a suitable contact cleaner, and given a shot of DeOxit. Any socketed ICs are pulled out and the socket contacts cleaned in a similar manner.