Yep, it is pretty clearly the big E. Even if one could not see it clearly it would be obvious that it has to be the Enterprise as you want the eighth character and not a random starship or a shuttle (we already saw a shuttle diving into water
in VOY's Thirty Days
and while this was great on the small screen it wouldn't be visually orgasmic on the big screen) to be the star in a diving scene.
On a side note, perhaps it is just a kind of stupid Vernes echo but I think that anything with water is great in Trek. The above mentioned episode with the water planet had this little-boy-read-an-adventure-novel atmosphere and the Xindi-Aquatics in ENT were fascinating so I appreciate that the new movie wil feature a diving scene with the Enterprise.