It's time to get your feet wet! Explore the mysterious underwater ruins while searching for rings and things. When air gets low, a countdown begins - gulp the big air bubbles to replish Sonic's oxygen before the countdown reaches zero.
— Description, Sonic Blast US manual
Mostly following the same rules as other water-based Zones, the player must inhale air bubbles to prevent from drowning, but if there are none nearby, then Sonic/Knuckles can jump into a pipe for the same effect. There are also invisible water currents in this stage which should be avoided, as they will pull the character to different areas.
At the end of Act 3, Dr. Robotnik will show up in an egg-shaped submarine. This battle is fought entirely underwater. This boss attacks by firing harpoons aimed at the player from an underside-mounted launcher.
If the harpoons strike the ground, they produce a single Air Bubble - this is the only form of oxygen available during the fight, so the player must be sure to take advantage of it. The submarine's cockpit is its weak point, which must be hit eight times to destroy it.
- Blue Marine Zone is one of only two Zones in Sonic Blast to have water, the other being Green Hill Zone.