The ocean theory would require a global sea, around 30 kilometers below the surface, to explain the strange wobble. However, the scientists reckon that—given the surface conditions of the moon—it's more likely that its core is an unusual shape.
If it is a result of water, it won't be the first moon in the Solar System to prove damp. Enceladus, for instance, jets out water at its south pole, while Titan has a network of rivers and lakes—though they're filled with liquid ethane and methane, not water.
Further modelling and inspection by Cassini will likely decide which theory is most likely. [NASA]
source: gizmodo.com by Jamie Condliffe