The 20-year-old man was sitting on a railing smoking a cigarette when he lost his balance and plunged into the water.
Staff on the Birka Paradise threw out a life ring but the rescue effort was hampered by the simultaneous departure of the Tallink Romantica. The current generated by the ship’s propellers pushed the young man northwards.
A diver who witnessed the events jumped in to the water and swam out to the man. The two men were later picked up in a small boat.
Both were taken to hospital to be treated for minor injuries.