Pregnant women in their third trimester often dream of swimming in channels or downhill, while at conception women can dream of fish, or fish swimming up narrow channels. For Freud, dreams of swimming represent memories or wishes to be in the womb again, and may occur at stressful times when reassurance is needed. As a movement, it is one wherein you are making headway under your own power. Since you are in water in could refer to emotional energies. Becoming aware of unconscious material.
Any resistance that you encounter while swimming can symbolize in your dream difficulty with dealing with emotional issues. Resistance to fool hardy behavior (sink or swim).