Swimming fitness is swimming fitness. It makes little or no difference whether that fitness is gained in the pool or open water. fitness is fitness is fitness. However successful open water swimming is a skill that can be learned even while training in the pool.
Open water skills such as sighting can be practiced in any body of water. Take time on your long straight swims to practice the form of lifting you head to sight. The less movement with the upper body, the easier it will be to lift out of the water to sight. Additionally, use the power of the pull to drive the chin forward in the sight. Avoid pushing down on the water to lift the head. Long, straight, solo swims provided a great chance to practice sighting. It is also a great chance to used to the boredom and focus challenges that are associated with long open water swims.
Rough water swimming is also a skill. Unintentionally, many masters classes provide rough water and crowded swimming conditions every day of our training. Practice being hyper-aware of the stroke you are using in these conditions and get comfortable being uncomfortable. Practice swimming slower and easier in groups. The tendency is to go harder when we feel crowded and it will take practice and focus to swim your speed.
key to open water is consistency of speed and repeatability of
stroke. So practice holding a consistent stroke and pace in the pool
and that will translate to the open water swims. It is essential to focus not just on what your time is for a 2oo, but rather how you split a swim. If the back side of the swim is significantly slower than the front, it is unlikely that speed is sustainable. Practice "back-halving" swims. In other words, have the two halves of swims be the same time or even faster on the second part. This ensures that you are training at a sustainable speed.
The final thought is that open water swimming is also
about the ability to change speeds, both increasing and decreasing.
Buoys, running starts and exits require the ability to both speed up and
slow down. In fact, in mass start races it is essential to be able to start fast and then settle into your pace. These speed changes need to happen with the same type of stroke in order to maintain efficiency. Otherwise, you will find that you are using a massive amount of energy to swim your pace because the stroke has become inefficient. The pool provides us with an easy way to measure your stroke count and speed. Using these metrics, you can determine how our speed changes are affecting your efficiency of stroke.