IPA: /ˌsʌbəˈkwætɪk/
KK: /sʌbəˈkwætɪk/
Relating to or existing under the surface of water.
The subaquatic plants provide shelter for many fish species.
Subaquatic → It is formed from "sub-" (meaning under) and "aquaticus" (from Latin "aqua", meaning water). The word describes something that exists or occurs under water.
Think of being 'under' ('sub-') the 'water' ('aqua') — that's why subaquatic refers to things that are underwater.