Jasmine,

The figurine is plastic. The "water" is piping gel (you can get it at any craft store that sells cake decorating supplies) with a little blue coloring in it. Just chill the iced cake first before spreading it on so the frosting doesn't get mixed up in the piping gel.

I sprayed the sides of the cake with blue and green spray color (you can get cans of this at the craft store, too), then used leaf tip 352 to make the "Seaweed." The "rocks" are a round tip, probably tip 4 or 5.

I've also made other cakes with "water" and "sand." Just use brown sugar to make sand. You can also mold white chocolate candy melts in shell shaped candy molds to make shells, too. I'm sure I have some beach themed cakes on here somewhere.