PLAYERS: Awesome. pretty cool. Been in this sea forever, our legs are all shriveled.  Let's start!
ME: Ok, yea cool. So.....why are you here and where are you going?

FWIW, this is exactly what I did in my first game. Except it was way worse, because I had no setting at all. I literally started the game like this:

GM: (turns to player A) What are you doing?
Player A: Sleepwalking!
GM: Where?
Player A: In a graveyard!
GM: (not much I can do with a sleepwalker. Turns to player B) You wake up and Character A is missing. What do you do?
Player B: Look out the window. Do I see him?
GM: Roll discern realities...

Blah blah etc. Once I got them rolling dice, they soon failed rolls, and we soon had a burgeoning zombie apocalypse. All I'm saying here is that this CAN work, it worked for me though it was admittedly a little rough. It may have helped that I was playing with teenagers, not jaded old timers with assumptions and expectations. Having something like a Dungeon Starter would make it easier as at least it gives you something to stimulate your imagination. I was initially drawing blanks which kind of sucked.

If I were going to use the shallow sea I think I'd start with a soft move. Maybe just present them with an impression that encourages investigation. For example, "You are wading thigh-deep in the warm waters of the shadllow sea. You approach a group of houses, raised on poles above the water. What do you do?" Now just let the players make moves and drive it forward.