No one can argue Dara Torres has great arms. Swimming freestyle or butterfly are great exercises. But if you cant swim (or dont like the monotony of laps), try these exercises Deck press: Start in the shallow end of the pool (about 34 depth) and place your hands on the side with arms bent. Press your arms straight and lift your body to hang along the edge then lower to return to the water. Try not to use your legs and jump but really focus on using your arm strength. Perform 15 repetitions.
Water fly: Standing in shoulder depth water, place your arms to side, thumbs up. Keep fingers closed together and arms straight as you push the water to bring arms closed in front of you. Turn your thumbs down and press your arms back to starting position. Perform 15 repetitions. This exercise works both chest and rear delts.