I need to ask you some questions about your dream and your waking reality. What is your gender, ("another man" sounds like you're a father), your age, and your living situation: Are you living with the other parent of your daughter? Is there anything about your living arrangement with your daughter that could make losing her a possibility--even if it's not realistically likely?
If there's not a threat (in time-together, or in spatial location, or in emotional closeness) to your relationship with your daughter, then she might be a symbolic image instead of a representation of her real self--esp if your real daughter is now older or younger than the girl in your dream. A dream-video like this one would be more common for a mother's than a father's dream, unless you are a single father.
so your current life situation and your history with your daughter are important information I need to provide a good interpretation. Also, can you think of any recent event(s) or thought(s) and feeling(s) that seem related to the dream--and thus could have triggered it?
Further questions: What were the most surprising or shocking moment(s) in the dream? (I'd guess 1. daughter's missing, 2. mum appears.)
Were there any more scenes, fragments or details in the dream? Did you change into your street clothes? If so were they work clothes, dress-up, at home? When you jumped into the pool were you wearing clothes? (or unaware of clothes?) Was "another man" wearing clothes or not?