Not to revive an old thread, but I have had the same problem with my oil light coming on. So, in case anyone else is searching for similar information, I'm adding a post for that reason.

My oil light has come on, exactly as described above, on 2 different occasions. Both times, there was deep water involved, and the light came on at first, and then slowly dimmed and went out.

The first time it happened to me, I was wheeling though water up past the sills.

The other time was driving in the rain, through an empty parking lot late at night. I came across a rather large puddle, and decided to go storming through it. My second drive through produced the oil light coming on again.

In both instances, I stopped immediately to check the oil, and both times, the oil levels were fine.

My assumption is that water is getting into one of the sensors, as was mentioned above as well.

Anyways, all that just to say that it doesn't concern me as much as it did the FIRST time that it happened, and that it seems to be normal.

If you can call something like that "normal".

Regardless of how and why it happens, when the light come on, you should always get out and at least check that nothing is leaking, and that your oil levels are ok.