The baby sign for swimming looks like your are doing a few breast strokes. Take both flat, open hands and hold them out in front of you, then pull them apart and draw them back together. Repeat the sequence in small, circular motions.
If your baby loves the water, teach them the swimming sign before you both take a dip in the pool or by the shore.
This is a useful flash card taught best in conjunction with other swimming and water-related flash cards. Many parents have their babies take early swimming lessons to prevent pool accidents.