Most shark party ideas assume you have a pool. Most people do not. The theme survives fine without one.
A blue tarp, sheet or paper tablecloth on the floor or garden instantly becomes "the ocean" for games that need one — step on it and you are swimming, step off and you are safe. Children accept this reframing instantly; adults tend to overthink it.
Hide small toy sea creatures or shark-shaped cutouts around the space for a search-and-collect game. Same mechanic as every other theme here, and it is popular for the same reason: a container to fill and a reason to move.
Cushions or hoops scattered around the room as "safe rocks", with the blue tarp as the water between them, gives you a ready-made active game with no equipment to buy.
Frame it as sharks who are the heroes of the party rather than a threat — "help the shark find its friends" reads very differently to a nervous four-year-old than "watch out for the shark".
If one is nearby, yes — it gives the theme something real to point at, which none of the craft activities can.
Part of our guide to Birthday party for one obsession.