Water ditto?

Yes, but was probably an older Ditto caught as a Magikarp. I think the Ditto search glitch was fixed at some point and only still affects Ditto that were caught while the glitch was around.

mackcab: Try doing a search for "+ditto" and it might also bring up Magikarp and Gyarados, which would indicate that the search is treating that Ditto as though it were a Magikarp.