https://prnt.sc/lrlec1
Water can move underwater. Basic science.
A toad can certainly move underwater, as can a shark.
While not an everyday thing I see no reason why a hamster couldn't, in theory, move underwater - especially if not alive.
Having the name Melinda would be no obvious reason to not be able to move underwater.
A volleyball might be a bit more of a long shot but it could be deflated or held by Melinda with a hamster inside. Not entirely impossible.