It depends on how large, what temperature, and what type of metal. If there's enough latent heat in the quantity of metal to flash boil a significant fraction of the water, you're going to have a bad time. If you're literally dropping it in the ocean on the other hand, then you'll get a brief but impressive geyser and the fire will go out.
(Unless this is an alkali metal we're talking about. In that case you'll just get a "vigorous reaction" of a size proportional to the quantity of metal. Ex: https://www.youtube.com/watch?v=cc6W6SptLvU)
