This is why I love how organized the Chicago Triathlon is.

What they do 1 month before the triathlon is they have weekly open water swim clinics, where you do a test aquathlon ( swim/run). This allows beginners or inexperienced open water swimmers to get acclimated to the roughness of open water ( especially in Lake Michigan) before doing the triathlon so they will know what to expect. Even experienced open water swimmers do them when they have been out of open water for a long time.

A lot of people train in the pool, where the temperature is controlled and the water is clear, so it is very calm and easy to swim in. Then they go out and do a triathlon, and find that it is a totally different environment. A 360 degree space that is in constant motion, and the temps are very cold.

Get your laps and endurance in the pool, but get your experience in open water. 2 swims in the pool and one swim in open water per week was my training method for the tri and aquathlons that I did.

My main issue with open water is the temperature, due to my body being more on the lean muscular side. I don't have a lot of body fat. That's great for being on land, but terrible for being in the water. There are no muscular marine creatures. They are all fat with low body density, so they have great buoyancy and heat insulation. So I get cold extremely fast in open water, so I can only stand maybe 45 mins to 1 hour before the chills come on, and the body loses heat quicker in water than in air. I have to always wear a wet suit or a tight water base layer in open water for insulation and warmth, and swim no more than a mile or 2. Hypothermia is no joke and happens quickly, which is why Tris can be very, very dangerous....

And it usually takes me a few weeks to get re- acclimated with open water every year. I haven't been in open water for close to 2 years, so I would need a good month to get comfortable again...I also swim with a buoy in tow, with a rope wrapped around my waste just in case cramps settle in, and I need to rest, or If I get sick.

The key is, believe or not, you have to chop the water. You have to swim just as violently as the waves are. The water will not allow you to be graceful like it is in the pool. Quick choppy strokes, bilateral breathing, and site every 2 to 3 stroke cycles....open water is tough shit