Tidal Tempest

From the Sonic News Network, the Sonic Wiki

Tidal Tempest is the third round from the game Sonic the Hedgehog CD. It follows Collision Chaos and precedes Quartz Quadrant.

It is an underwater region at the base of a volcano. Stone pillars are present and the water elevation is normal. In the past it is an underground cavern that has been untouched by mankind or machinery. The water level is fairly low here. The bad future shows an over-industrialized, nonfunctional water plant. The water here is polluted and is unsafe. In the good future is a fully operational, turquoise aquarium that harbors much plant life and aquatic life. The water level is at it's highest point in both futures.