I think he's trying to say that he's had two rigs downchecked for charging issues after fording - because the alternator is mounted low, and probably got dunked.
1) Try rinsing the alternator with clear water after the crossing, but be sure to leave the engine running! The flush will help get crud and such out from under the brushes, but you have to make sure it gets dried out (the brushes are loaded against the comm rings with coil springs, and they can and do rust...)
2) Could you verify that code? OBD-II SAE codes take the form of <letter><0 or 1><three numerical digits>. The letter tells you what general system (P = Powetrain, B = Body, U = Network,) the <0 or 1> tells you what sort of code <0 = SAE-defined, 1 = vendor-defined,) and the other three digits are the specific code.
So, is it P0682, or P1682? They would be two entirely different issues, which is why I don't want to guess...