So, how do you make a beach theme formal?

my thought, without reading the other answers:

big white flower ((in your hair - why don't more girls put things in their hair? barettes are absolutely the cutest - seriously, very cute.)) --

or a flower-y (literally real flowers) headband -

braids are pretty beachy to me (those pull back ones). but just wear your hair how you like it best... I would guess that's your option. (guessing my way through this =))

dress: airy or shoulder cardigan why combo/dress.

my guess: cross a bonfire out-fit with a beach wedding dress/thing.

mermaid seashell breastcupps are optional, but preferred =) (again, perfectly fine daily/non-Little-Mermaid wear in my opinion =)). pictures would be fun =)

the more formal, the less 'showy' I would guess. but it's a good rule to bend to the point of breaking, haha. ...white seashells! if you do ;) - joe

Two words: Wetsuit Kimono

Wear a bikini UV pain all over your body aaaaaaaaaaaaaaaand a bow tie!
The tie signals formality.

Wear a mermaid dress in a beach/ocean type color like light blue, aqua, coral, or even gold. Then give your hair beach waves and put it to one side of your head. Attach a flower or seashell or starfish to it.

At least, that's what I would do if I went to a dance with that theme.

Argh, I posted a really long response last night and it didn't go through! Let me try again.

floral floor length wrap dress and pretty intricate jewelry

wear a mermaid dress! :D lol