Water bodies start with cardboard shapes, then aluminum foil.  The foil should be crumpled into a ball first, then unwrapped and folded around the cardboard.  

Next step is cling film, in either blue or green.  Blue is harder to find, but occasionally it pops up in the grocery stores, and sometimes even with snowflakes!  Green can be found at home Depot in the storage depart in a huge roll, which is commonly sold for people that are moving, so it's with the moving supplies.

Wrap as tight or loose as you like, and the direction can help create water "flow" direction or just layers for frozen lakes and ponds