According to Steve Tarpininan easy, long swims are not preferable even during the off-season and winter . Training with easy, long runs and bike rides is preferable, but easy, long swims is not. Your swim technqiue will become worse and you will actually get slower. In swim training, you need to add speed all-year round to your training regimen. You can train hard every single day when it comes to swimming. However, you cannot do that when it comes to biking and running. Why? Because the water helps you recover; the hydrostatic pressure and cooling effect of the water helps the body recover. Swim experts do one hard practice in morning and one easy one in the afternoon/evening. Steve recommends 3 swim trainings per week – one hard, one medium and one easy swim that is more focused on technique.
One swim training method is half pool sprints which are great to do year round. As you are getting ready for a race, do more half pool sprints. One method is to do a streamline push off in the pool, do not breathe for 8 strokes and swim as fast as you can, and, after the 8th stroke, begin to breathe and swim really long and easy to the wall.