Creatine is a great way to get more out of your workout and build lean muscle. But is it appropriate for swimmers?
Swimmers need immense muscular strength and endurance. Not much research has been conducted to date, so it's hard to quantify the benefits of creatine for swimmers. (In general, see Athletic Performance Benefits of Creatine.)
Creatine extends the ability to continue repeated high-quality efforts for 25 meters. [1, 2, 4, 5, 8] Thus, you would think it would help you maintain a more powerful stroke. However, this may only work when efforts are extremely high-intensity and require long rest periods. 
Conflicting evidence exists, as performance has not been improved, despite the alteration of blood markers in short-distance repeat sprints. [7,10] Some studies show improvement after single sprint performance [6, 7], while others do not. [2, 4, 9, 12]
The evidence is obviously inconclusive. However, the use of this cheap, naturally occurring substance appears to improve repeated high-intensity swimming performance, similar to a workout or competition. (See Is Creatine Safe and Effective for Young Athletes?)
In the end, supplementation is up to you and your support team (coach, family, etc). You must weigh whether it's worth your money and effort to take a creatine supplement. If it works for you, that's great. If not, you will continue performing at an elite level without the supplement. (Read the YOU Docs: Q&A on Creatine.)
Remember, if you are going to be drug-tested, make sure your supplement is approved by the International Olympic Committee with the HFL stamp of approval.
 Ricketts, J. C., & Zachweija, J. J. (1999). "Effects of creatine supplementation on swim power." Medicine and Science in Sports and Exercise, 31(5), Supplement abstract 1243.
Peyrebrune, M.C., Nevill, M.E., Donaldson, F.J., & Cosford, D.J. (1998). "The effects of oral creatine supplementation on performance in single and repeated sprint swimming." Journal of Sports Science, 16(3), 271-279.
 Carl, D. L., Alperin, N., Kochendorfer, K., Stieger, J., Andres, F., & Broadley, D. (1999). "Effect of oral creatine and caffeine on muscle phosphocreatine resynthesis in competitive swimmers." Medicine and Science in Sports and Exercise, 31(5), Supplement abstract 1283.
 Leenders, N., Sherman, W. M., Lamb, D. R., & Nelson, T. E. (1999). "Creatine supplementation and swimming performance." International Journal of Sport Nutrition, 9, 251-262.
 Grindstaff, P. D., Kreider, R., Bishop, R., Wilson, M., Wood, L., Alexander, C., & Almada, A. (1997). "Effects of creatine supplementation on repetitive sprint performance and body composition in competitive swimmers." International Journal of Sports Nutrition, 7, 330-346.
 Selsby, J. T., Beckett, K. D., Kern, M., Devor, S. T. (2003). "Swim performance following creatine supplementation in Division III athletes." Journal of Strength and Conditioning Research, 17, 421-424.
 Selsby, J. T., Beckett, K. D., Devor, S. T., & Kern, M. (2001). "Swim performance following creatine supplementation." Medicine and Science in Sports and Exercise, 33(5), Supplement abstract 1159.
 Juhász, I., Györe, I., Csende, Z., Rácz, L., & Tihanyi, J. (2009). "Creatine supplementation improves the anaerobic performance of elite junior fin swimmers." ACTA Physiologica Hungarica, 96, 325-336.
 Dawson, B., Vladich, T., & Blanksby, B. A. (2002). "Effects of four weeks of creatine supplementation in junior swimmers on freestyle sprint and swim bench performance." Journal of Strength and Conditioning Research, 16, 485-490.
 Mendes, R. R., & Tirapegui, J. (2002). "Effect of creatine supplementation on supramaximal exercise and body composition of university swimmers." Medicine and Science in Sports and Exercise, 34(5), Supplement abstract 806.
 Jacobs, K. A., Leenders, N. Y., Sherman, W. M., Nelson, T. E., Lamb, D. R., & Miller, E. C. (1998). "Creatine (Cr) supplementation and swimming." Medicine and Science in Sports and Exercise, 30(5), Supplement abstract 1506.
 Mujika, I., Chatard, J. C., Lacoste, L., Barale, F., & Geyssant, A. (1996). "Creatine supplementation does not improve sprint performance in competitive swimmers." Medicine and Science in Sports and Exercise, 28, 1435-1441.