I am a certifiable fish and not a member of EN, but I spent too many winters of my life swimming already, there is nothing LESS appealing to me than getting into a cold pool when I'm already cold. I have tried it both ways, suffering through winter swimming at the start of my tri career and (for the past 3 seasons) not swimming at all from my last race in August until after the new year. I spend all the extra time in the fall/early winter improving my weakness (the run) and mix in the bike for low-impact aerobic work. This has really paid off for me, you never realize how much better training can be when you aren't trying to juggle 3 sports at the same time until you finally break free for a while. Every year when I have to add swimming back it instantly becomes challenging to stay consistent and fit all my training into my week. I personally think it is nuts to keep working on three sports if you can cut it down to two due to relative strength. I have improved my run dramatically in these 5-6 month breaks from swimming, and every year I am back to swimming form almost instantly. I know a lot of people don't want to hear it, but swimming really is all about technique. Once you have good form you can build your aerobic base in other sports and it only takes a few weeks for swimming to catch back up.
That said, if swimming is your weakness (or if you enjoy it) I would probably not recommend taking a break for more than a month, cut something else instead. I would also avoid cutting out running if you are injury-free just because it can be challenging to build that running volume back up if your body isn't used to the pounding. So basically I say cut swimming or cycling in the winter, if they are both your weakness then pick one to focus on this off season and work the other one next off season.
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