For posterity, here are great events of my Walden Pond swimming at age 49 during the summer of the great drought, 1999.

Great distances
  1 @ 6 miles#
  2 @ 4 miles
  3 @ 3 miles
~90 @ 2 miles
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# Mile is defined as 2 lengths or roundtrip from main beach to favorite steps & back.  The actual distance is probably a little less than a mile (up to 10% less).

Great times
  10:52^,10:58,11:09,11:12 Single length*
  23:10^ Single roundtrip
  46:52^,47:08,47:14 Two roundtrips
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^ all-time best
* either main-beach-to-steps or steps-to-main-beach, about 1/2 mile

Great single events
  3:03:10 for 12 lengths with Keith, Rick, and Mike Hurley, 5:38am-8:41am, 22Aug
  1:38:29,1:38:43 for 2x8 lengths (12:19,12:20/length), Sat and Sun, 4-5Sep

Great details
  1. I'm generally 15-20 s slower going down than coming back.
  2. The 6-mile swim was fun; last length in record time!
  3. Two collisions (PeterII and unknown).
  4. Good fog events.
  5. Dirtiest trick was swimming underwater to scare Mike.
  6. Water was warm well into September; still no bathing cap as of 21 Sep.
  7. Lots of bare beach, so each length is a few yards shorter than last year.
  8. Great set of swimmers: Mike Gates, Mike Hurley, Keith Meliones, Cedric
(Rick), Peter I, Peter II, Jennifer Dutton, all those triathletes.
  9. Birthday swim of 2 lengths with Emily and Melanie

Great Future
Next year I'll try for the Boston Light Swim and 100 x 100 yds.  Maybe 10 miles in Walden also.