I've mentioned before that I'm an art supply hoarder. People bring me stuff all the time and I put it away for "safe keeping" (read: in some unmarked bin somewhere in my classroom and I come across it 2 years later).
I did this project at the end of the year when I found a bunch of foil, patterned papers, and pieces of foam. What was I saving this for?! I must have been envisioning a project like this :)
We used some floppy foam paintbrushes to paint the "water" in the background. We used tissue paper as an overlay for the seaweed and sand. I had the kids use leftover foam pieces for coral and some fish, we drew on foil with colored sharpies for other sea creatures. I let them go nuts in my random bins for buttons, beads, ribbons, pearls, yarn, pom-poms, etc for other sea creatures. They had a blast, and I love the creativity that came through!