However, there are a few idioms that use similar imagery or concepts related to water or the ocean:
* "To be in over your head": This means to be in a situation that is too difficult or complex for you to handle.
* "To go down with the ship": This means to remain loyal to a cause or a person, even when it is failing or sinking.
* "To be adrift": This means to be lost, confused, or without direction.
* "To go with the flow": This means to accept things as they are and not resist change.
While "under the sea" itself is not an idiom, it can be used figuratively to suggest a feeling of being overwhelmed, lost, or trapped in a situation. For example, someone might say "I feel like I'm under the sea, drowning in paperwork."
It's important to note that the meaning of a phrase can vary depending on the context. If you are unsure about the meaning of a phrase, it's always best to ask for clarification.