The idiom a fish out of water means an individual experiencing discomfort or unease in a specific environment. It conveys the sense of someone who is not in their usual or natural element, much like a fish that’s not in its natural water habitat. Collins Dictionary says, “If you feel like a fish out of water, you do not feel comfortable or relaxed because you are in an unusual or unfamiliar situation.” Moreover, the Cambridge Dictionary states that the idiom means “a person who feels awkward or unhappy because they are in a situation that is not familiar or because they are different from the people around them.”

Source: Grammarist