Hi @blox ,
The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the tracker's operating design and could damage the components. The corrosion starts immediately and is ongoing until it is completely cleaned away
First do not try to charge or to turn on your device and then remove the battery as soon as possible to minimize any further damage.
Then you need to dis-assemble the rest of the device and clean all the affected parts using Isopropyl Alcohol 99%+ (available at electronics parts stores) to remove all traces of corrosion and water. If possible do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, can contain additives and is not as effective. If you do have to use it check the label to verify the amount of IPA. The higher the percentage of IPA the better
Here is a link that describes the process. Electronics Water Damage
As always with electronics, especially surface mounted pcb be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board. The ends of any flex cables and their connectors need to be cleaned as well
Hopefully after you have done all it might possibly work correctly again.
Here is a teardown video that may help, although maybe not as it doesn't show the device being reassembled.