Yep, Water Wurm is a wurm. And the only mono-blue one ever at that! Makes you wonder if they made a mistake with the typing... (That’s suspiciously similar looking, isn’t it). But it does mean there’s a wurm for every colour, so even your most control-y player has no excuse not to include one.
It’s from The Dark, the fourth set ever. A 1/1, super occasionally 1/2 for 1 mana is... really not very exciting. But Ron Spencer’s art has charm, fits the frame nicely, and is a good reminder Wurms can be reptilian but also, uh, something you’d expect to find in your gut sometimes.
The real question is, how do you make it reliably a 1/2? If your playgroup is just hardcore Wurm tribal players you’re probably not going to see many islands on the other side of the field. That’s where Quicksilver Fountain (and its ilk) come in. Yes, you’re gonna massively mess with everyone's plans but they’ll concede quickly upon seeing you cast Reflections of Littjara, then four Water Wurms. That’d be 8 power and 16 toughness for just four mana!