"All right, I think this has gone on long enough. Gimme that, brainless things beneath the waves, this chest of yours will be great plunder!"

Spoiler
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Am I close enough to the chest-carrying zombies yet?

If I am: Strength check to rip the chest away from them: (1d20+6)[26]
(Or would you want a disarm check or something instead? Sleight of Hand? )

If not: Swimming closer! (1d20+13)[27]