This article on Active.com discusses tapering for a distance swim:
Open-water tapers need not last two or three weeks (the length of a typical pool-swimmer?s taper). One week is usually plenty of time to feel rested and recovered if you are used to endurance training throughout the season. In fact, an open-water swimmer preparing for a five- to 10-mile race need only pare down the distance and intensity of his workouts maybe three days before the event.
In such extreme high-endurance events, I prefer to take the day prior to the race off completely (as long as I have enough time to warm up 30 minutes the morning of the event itself). This full day off forces your body to rest and recover (even if you think you may not need it, you might), and your consistently fatigued muscles will feel fresher with a full 24 hours of idle rest.
In preparing for this coming weekend’s Great Chesapeake Bay swim, I’ve spent nine months on an entirely haphazard, three-day-a-week-except-when-I-was-too-tired-to-get-out-of-bed solo training program. I’ve tried to work on endurance and some speed, but mostly endurance, on the grounds that getting across will be more important than getting across fast.
With one week to go I did a roughly full-distance swim, broken out as 6000 yards in one pool and, later in the day, 1600 meters in another. All at a fairly easy pace.
With five days to go, I did just under 3000 yards, mostly in 300 sets, again at a steady but not exhausting pace.
Two days before the swim, I plan to do a very easy one mile, probably at the Richmond Tri Club Friday night swim, so I can get in a little last-minute open water work, and test out my new goggles.
The day before, I’ll just paddle around in the pool to stay loose.
I don’t think there’s any warmup at the swim, so I plan to try to do a little early morning warming up in what I expect will be a tiny hotel pool.
And then we’ll see….