Jesus Christ, the caltrops! But that aside, unfortunately it has probably despawned with the boats. It should just get displaced if the boat spawns on top of it, but something must've gone wrong, and I can't tell what from the save.
Sorry for the inconvenience, but unless I'm missing something, that jet ski's lost
.
That said, I could spawn you a new one as a replacement. Want it on this save or do you have a more recent one?