This is an excerpt from Open Water Swimming by Steven Munatones.
Training in Rough Water
There is no substitute for experience in rough water. Practice will not make perfect, but it will make swimming in rough water much easier. Instead of always training in flat conditions, occasionally swim when the winds come up so you can face heavy surface chop.
The cliché "Prepare for the worse and hope for the best" is appropriate for the open water swimmer. If you train in rough conditions, you will be ready for anything on race day. Conversely, if you train primarily in flat conditions or in a pool, you will be ready for nothing but flat conditions on race day.
If the conditions are rough, swim parallel to the shoreline during your open water workouts. If there are whitecaps, swim in one direction for half of your swim and in the other direction for the other half so you practice with the turbulence hitting you from both sides.
It is easier to breathe away from the oncoming surface chop. Determine your most comfortable breathing pattern so you can avoid having each wave slam into your face as you breathe. Breathe farther back than normal by slightly moving your face backward as you roll your head to breathe. Position your mouth in the area under your recovering arm and armpit. Swim with your mouth closed when your face is in the water, except when you exhale moments before your head turns to breathe. This will help you avoid swallowing water. If you are not accustomed to swimming with your mouth closed and exhaling when your face is in the water, practice during your pool workouts until it becomes natural.
Facing Surface Chop
At times, you cannot see that you are being pushed by tides or currents in the open ocean. But, you can always feel the effects of wind and surface chop. From a mental perspective, surface chop changes how you feel. From a physical perspective, it can change the way you swim.
Frustration is natural when swimming in rough water. Even if you are being pushed with a current, swimming into surface chop is demoralizing and difficult. In rough water, your mental focus and determination must increase just as your physical effort increases.
When the water is choppy during a race, pay close attention to your competition. Someone can make a move on you while you are focused on fighting the elements.
You can tell that a current is with you by observing the shape of the surface chop. When the wind is blowing with the current, the wave action is smoother than when the wind is blowing against the current or at right angles to it. When the current is flowing against the wind, the waves become steeper and can turn into whitecaps quickly. As a general rule of thumb, whitecaps occur at 18 knots (1 knot equals 1 nautical mile per hour or approximately 1.15 miles per hour). If the wind speed is 15 knots and the oncoming current speed is 3 knots, the cumulative total is 18 knots, and you will face whitecaps.
Ocean waves can be intimidating during onshore starts and finishes. If you do not have experience with bodysurfing, watch some online videos of bodysurfers and then go to the beach and try to repeat what you saw. When you are swimming into shore and feel the wave gaining momentum behind you, try to time your maximum speed to peak as the wave's surge picks you up and powers you forward. As the wave lifts you up and crests around you, place one hand in front of you and one hand at your side as you slide down the wave. Keep your head up and kick as you skim down the face of the wave while you allow the wave to push you forward. If you feel the wave going past you, kick harder while you swim with one arm stroking fast and one hand still in front of you. This will enable you to gain the maximum benefit from the wave and resultant whitewater. After the wave sweeps past you, start swimming again.
Before the race, examine the shore break and count the number of seconds between waves. This will give you a sense of how much time you have between the waves, what to expect, and how fast you need to keep moving through the surf zone.
If there is sizable surf as you head out, the most important thing to do is to dive under each wave and head toward the ocean bottom when you are underwater. While you are underwater, kick hard in a streamlined position with both arms held straight out in front of you. When you pop back to the surface, immediately lift your head to look for the next wave.
If the water is rough and you have to fight through the surf, you may want to put your goggle straps under your swim cap or tape your goggles to your swim cap. You can also wear two swim caps with your goggle straps between the first and second caps.
Understanding Tides and Currents
Current-positive (i.e., current-assisted or current-enabled) swims, in which the currents are with you and pushing you forward, are generally easy. Conversely, current-negative (i.e., current-handicapped or current-impeded) swims are tougher to handle, especially when you are aware of their negative effects on your progress.
Swimming in rivers, estuaries or bays, in and out of coral reefs, or around islands can be tricky because of the tides and currents. In rivers, bays, reefs, and ocean coves, the water depth and flow change constantly. In general, water flows faster where it is deeper, but there are exceptions. If possible, research the conditions before every race, especially where tides and currents are significant. Experienced boat pilots are often the best source of information, but it is best to seek more than one person's opinion. Surfers, kayakers, local swimmers, and lifeguards are also helpful and generous with sound, accurate advice.