[Kiwi]

Assuming that you somehow overcame the challenge of setting up the pool/field, if the competition was still two alliances of three bots, it seems like they'd interfere a lot with one another. Bots would have to have bumpers all over, because they'd all be travelling in three dimendions rather than moving on the plane of a non-aquatic field.
After two minutes of six bots propelling themselves around in a pool about the size of a regular field, there'd probably be waves to contend with -possibly enough to tip over a less stable floating bot.
The aquatic robots would probably work like either boats or submarines, and with a random combination of both on the field, the designers of the game would have to be careful with the rules. Would it be okay for an underwater robot to accidentally or intentionally capsize a floating one?
Maybe lifting the other bots out of the water would be the end game challenge.

Pros:
- we'd learn underwater electical design, in six weeks
-creative thinking to overcome the logistical challenge of finding a practice field
-everyone who's ever speculated about a water game would be able to say a giant 'i told you it would happen someday!'

Cons: all of the above... plus it would be dificult to enforce gracious professionalism on the field, and any damage to the bots during the game would be harder than it already is to repair.