I'll say that shooting from a 'Zodiac' rescue boat wasn't an ideal platform, but thanks a million to the Charlottesville/Albemarle Rescue Squad's Water Rescue team for allowing me to ride with them. They couldn't safely get close enough to the swimmers for my purposes.
I finally decided to venture out near the start/finish carrying the 70-200mm with the 1.4x Tele-Extender (giving me an effective range of 156-448mm). The rope divider showed up a bunch for the 2nd heat of the 2 miler, because of the direction of the swim, but for the most part the pics were unbroken. I would have liked to get exactly even with the turn buoy to get both going and coming, but the water was over 5 feet there.
Needless to say, being chest-deep and holding about 5 pounds of camera out of the water for an hour wore my shoulders down, but the close-ups at that angle were pretty cool. I might build a floating platform to put the camera on when I'm not shooting next time! A big thanks to Dave Holland for a well-organized event, and for giving me the opportunity to be there.