You warm up before to start a training session and should before you start an Open Water Swim or Triathlon Swim Start.

Triathlon races are often early in the morning, especially for the long distance events, so getting your body and mind warmed up and focused can take some conscious effort. 

Benefits

A warm up prepares your heart and lungs gradually for increased activity which increases oxygen uptake by the muscle to prepare for the additional workload to come and ready to work efficiently.

Reduces muscle stiffness, less chance of injury, during and after and allow you to work out longer and harder.

Improves your coordination and reaction time, primes your nerve-to-muscle pathways to be ready for swimming, thereby improving your performance.

Its important to get familiar with your routine to mentally and psychologically prepared for the race. Having a warm-up that you’ve done before and has worked well for you in the past is something that can be a big improvement in how you approach the race mentally.This mental aspect is something that should not be underestimated because it’s definitely one of the main determinants of racing success.

I encourage you to find one single warm-up routine that works well for you, one that has worked well for you in a race. When you find it, stick to that routine. Try to make it a habit to do just that one routine and it will give you a mental edge in your racing.

You should start incorporating your warm-up routine in your training so that you know how to do it without even thinking about it when you get to your race.

If you are racing in cold water it is especially important acclimate to the water.

When you can not get in the water, I suggest as a dryland warm up.