Aqua Planet Zone, is the fifth zone of Sonic Chaos for the Sega Game Gear / Sega Master System. In keeping with the other stages of this game, Aqua Planet consists of two standard Acts followed by a shorter, third Act which contains the boss. Geographically, this Zone is located on South Island (as is the rest of Sonic Chaos).
Why it's called Aqua Planet is something of a mystery; but it's certainly aqua, with underwater sections aplenty - reminiscent of Hydrocity Zone from Sonic 3 and Knuckles. The Zone consists of crumbling, half-submerged ruins, from which ruby-tinted offshore oil rigs can be glimpsed in the background (these are presumably the Doctor's work). Aqua Planet is a stormy zone too, as the roiling clouds will attest.
||Dive into an underwater quest with fierce currents and treacherous tunnels. Hold your breath and grab air bubbles to survive. Countdown numbers appear over your head to warn that you're running out of air. The Sphere-o-Bot Boss awaits.
— Game Gear version manual
||Push open the hatches in the underwater tunnels and the current will carry you along, but beware of the traps ahead! If you go without air for too long, you'll see a countdown above your character's head. When that count-down reaches zero, you lose a Life. Replenish your air supply by jumping to the surface or taking a deep breath from big air bubbles that drift up from certain blocks.
— Master System version manual