Shamu's Deep Sea Adventures is an action game where players control Shamu the killer whale on a quest to save the SeaWorld theme park from the Greek god Poseidon, who plans to replace it with the lost city of Atlantis and take over the world.
The Game Boy Advance version plays differently to home console versions. Players guide Shamu across various levels using the control pad or stylus to swim, dash to defeat enemies, break objects, and jump out of the water. Instead of a health bar, Shamu needs to collect crystals to protect himself from enemies such as puffer fish, sea anemones, and the evil Kraken.
The gameplay involves navigating through levels filled with crystals, Atlantis tablets, and treasure chests. Collecting every four treasure chests unlocks a photo in the Art Gallery in the main menu. Temporary objective items are also present in each level, which can be kept in Shamu's inventory to use later.