Personally, I think this one's even stranger.
That said, though, I actually really like the idea of water-dwelling, non-water-type pokémon. The amount of variety in aquatic life IRL is
ginormous, and it'd be really cool to see even more of that variety reflected in Pokémon. If pokémon HAD to be water-type just because they're aquatic, then it would kinda hold that variety back, I'd say. Not to mention it just wouldn't be good for type distribution in general... I don't recall being a fan of all those water routes back in Ruby & Sapphire where EVERY SINGLE ENCOUNTER was a water-type. Besides, if you think about it, saying that aquatic pokémon have to be water-type is kind of like saying land-dwellers have to be ground-type (or perhaps that they have to be flying-type because they breathe air).
...Sorry for the spiel. Admittedly, I somewhat fell out of the loop on Pokémon during the previous couple generations, so I don't actually know how most people feel about this subject, or even whether or not I'm spouting nonsense. Let me know if I am, by the way.