Despite being based on the 1989 film, the game's plot bears little resemblance to it. The player guides Ariel or King Triton through underwater levels similarly to the game Ecco the Dolphin, and can move in any direction. Gameplay is identical regardless of character choice, and both feature two attacks for defeating enemies - a "normal" and a "special". Supporting characters from the film such as Flounder and Sebastian make appearances, and can aid the player in their quest.
There are a total of five stages, four of them regular. Each features a boss fight at the end, with the final boss being Ursula.