The position of the bears relative to the narrator and the person matters here.
If they are between the narrator and the person, that is they swim away from the narrator towards the person, then it is Snámhann na béir sall chuige or
Snámhann na béir anonn chuige.
If the bears are away in the distance and the person is between them and the narrator, that is they swim towards both the person and the narrator, then it is Snámhann na béir anall chuige.
If the target is between you and the bears but off at an angle then "swim over" is appropriate. "Over" can mean both "away from" and "coming towards". For example "Go over there" and "Come over here".