Need help with an activity for preschool children.?

Im a childcare student and i got to do a creative activity for preschool children that is creative and that's apart of the curriculum. The problem is the theme has to be about "under the sea" -so sealife and all that-, and i have not a clue on what i should do that is simple enough for them to do. Any ideas or activities a teacher has done in the past would be brilliant.