Cut out shark and fish shapes from foam and tape into a dollar store blue vinyl tablecloth. Hang up on the ceiling below a light fixture so that it hangs loosely (not to touch the light). This will give an underwater feel to your space!
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Do It And How 
I have my son’s 2nd shark birthday in a few weeks can you please tell me where or how you made your sea animals? I’m horrible at drawing.
Thanks in advance for any help you can offer,
Liz