Under Water?

I popped into the parish church to view this year's Christmas Tree competition and was mystified by the nautical objects on display.  Every year there is a competition, entered by schools and charities. Visitors make a donation to get tokens which you award to the trees you like the best.  The parishioner on duty explained that some charities were trotting out the same decorations every year, especially if they had done well.  So,  they have introduced a theme for the trees, which this year is  "Under Water".  That explains the fish, mermaids, octopuses , submarines, seals, starfish...........................