Oil light on dash coming on

I have a 1990 Supra Sunsport. I have had no trouble out of this boat yet and have owned it for about 2 years now. I took it out one last time in the fall and the oil light came on. I immediately turned the boat off and checked my oil. The oil is at the right amount. I then took the boat back to the dock. As soon as I come above idle it quits making the noise. The boat has about 350 hours on it. I know there are several things it could be but I am just wondering if anyone has ran into this before and found a solution. Thanks guys.