Rocket League is unabashedly riffing on BioShock in its latest free DLC update.

Entitled "Aquadome," the pack takes players to the bottom of the ocean, staging the game's trademark rocket-car ball sports in a huge underwater stadium.

Sharks and other marine life patrol outside the glass dome, whose design is fitted out with art deco flourishes to make Andrew Ryan jealous.

The DLC's marketing capitalises on the (unofficial) BioShock connection, too, sporting the same typeface as many elements in 2K and Irrational's classic series.

New cars - the aquatically-named Proteus and Triton - will accompany the free map, but will be premium DLC purchases.

The new content will land with the game's October update next month.