Because you can't speak normally while underwater, you can't cast spells with verbal components. So you also can't activate magic items that require command words. (https://rpg.stackexchange.com/a/77917/37116 )
The Wand of Wonder doesn't mention a command word though:
While holding it, you can use an action to expend 1 of its charges and choose a target within 120 feet of you. The target can be a creature, an object, or a point in space. Roll d100 and consult the following table to discover what happens.
So it should work. But what if it causes you to cast a spell with verbal components?