Aqua Lake Zone is the third Zone in the 8-bit version of Sonic the Hedgehog 2. As with other Zones in this game, Aqua Lake consists of two standard Acts followed by a shorter third Act which contains the Zone's boss.
Aqua Lake Zone fulfills the underwater theme for this game. The surface areas in Acts 1 and 3 sport an abundance of operational fountains and water features, while beneath the lake's surface in Act 2, crumbling ruins provide the hedgehog with a dangerous obstacle course. The air bubbles in Aqua Lake Zone are much larger than those in the Mega Drive games. Sonic can actually jump inside some of the bubbles and ride them all the way up to the surface; a gimmick which is featured prominently in Act 2. Tidal Plant Zone in Sonic Triple Trouble and Hydrocity Zone in Sonic Mania would later revisit the concept of riding in air bubbles. In both of those games, rideable air bubbles are created by stepping on buttons.
Act 2 features a Power Sneakers monitor in the Master System version, and is the only instance in the game which it appears. In the Game Gear version, it is replaced with a Super Ring monitor.
This is one of the more difficult levels, due mainly to the slowdown caused from being underwater, as well as the distance between air bubbles. The level is notable for featuring a gimmick that enables a spin rolling Sonic to bounce across the surface of the water like a pebble. The boss is the Mecha Ashika.
||Pick up speed and skim the surface of the lake, picking up Rings as you go. When you go under, don't go for too long without air, or you'll lose a Chance. Take a deep breath from bubbles that float up from some of the blocks. Or when a big bubble comes your way, use it to float toward the top of the screen.
— Sonic the Hedgehog 2 US Game Gear manual
||A labyrinthine zone in the bottom of a lake. Sonic has learned to move across the water’s surface but if he falls into the water, he still can’t swim. Because there is a countdown when you are incapable of breathing, don’t forget to grab a breath from a big bubble.
— Sonic the Hedgehog 2 JP Game Gear manual (translation by greenyvertekins)
||Taraban — Crab bots that move back and forth in a small area. Every once in a while they pause to fire flashing projectiles in either direction.
||Zaririn — Weird crustacean bots that swim back and forth in a small area. When they spot Sonic, they pause briefly to fire off a couple of flashing projectiles, then dash off the screen.
Chaos Emerald location
The Chaos Emerald for this Zone is a piece of cake. During Act 2, blue tubes transport the player in multiple directions. In the second tube, the player should hold down until they reach the gem. Continuing to hold after collection will lead to a secret life.