A hot engine under water will cool rapidly and the gases inside the crankcases contract, so if the crankcase breather is beneath the surface at this point then water can get into the crankcases and mix with the oil.
Depending on how deep the water was, in your place I would do the following (much of which is already advised above)::
1. Drain & replace the oil, including cleaning the oil filter. Ensure that there is no evidence of water remaining in the engine.
2. Remove the carb float chamber and clean the inside with fresh fuel. Replace.
3. Remove the spark plug, kick the engine over with the plug removed to ensure any water is ejected, then replace the plug.
4. If the air intake went under the surface then remove and dry the air filter element, ensure that the air intake is fully dry before replacing.
5, Check that the drain hole in the silencer is not blocked so that any water will have drained out as water in the silencer could make the engine sound strange. If unsure then raise the front of the bike to let any water drain out.
6. Spray all the electrics, liberally, with WD40.
7. Give it time to dry out.
Good luck.