Something that is subaqueous is located, done, or used under water.
Being subaqueous can be interesting for people who like to explore underwater.
Examples:
The fish live in a subaqueous world.
Divers use special equipment for subaqueous activities.
The subaqueous plants sway with the movement of the water.
The subaqueous tunnel goes under the river.
Exploring the subaqueous world is like visiting another planet.
The subaqueous creatures are strange and wonderful.