Swimming in a dream tends to reflect how you're handling your emotions in the moment -- moving through them with ease, or struggling against a current that feels stronger than you are. Smooth, confident strokes can point to emotional adaptability, while fighting the water often names feelings you haven't yet learned to move with.
The Fixed Stars are the most efficacious of all in their operations, for what actions they manifest or occasion are very great. - William Lilly (1602.-1681.)