I sent an email after the trip to a friend who's not a boater, and described this section of the trip to her.  We were on the Birkenhead River at "the low side of high" water.  Here is the relevant and unedited text of that email, save for the lucky paddler's name being removed:

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hey, here's a british columbia story (i just got back from two weeks kayaking out there) that puts a nice fresh color on the usual starry skies and snowcapped mountains and campfires and multiple bear sitings way the fuck out some logging road drinking beer stories after wicked cool kayaking -- that shit was day after day.  we were on the hardest run we did, and were in a bit over our heads.  no one had done it before, and it kept getting harder and harder.  it got described as the "west prong on crack" -- a reference to a run in the smokies called the west prong, and at the level we did it at that seemed perfect.  it had crystal clear water even to pools deeper than 8', and the rapids were stunning and continuous.  towards the end of the run where it got truly hard, my buddy _____ had a swim just after the entrance drop to a 100 yard long class V section.  he nearly got the stern of paul's boat who came after him, but couldn't.  me and todd had made the first drop and were scouting the rest of the rapid and had a great view of ____'s debacle.  i threw a rope to him but it was too late.  he swam head first between these two boulders and over a narrowing drop that to me and todd looked like a seive of death.  the last thing we saw was his feet.  truly, we each were thinking the worst for our buddy, and it was terrifying.  two or three long (long) seconds later ____ reappears below and claws his way onto a midstream rock -- from which we were finally able to rope him over to shore about 10 minutes later.

that's the set-up to the real part of the story.  see, ____ got a serious contusion/bruise just above his pelvic bone on his lower belly, and it looked like pure evil.  he kept paddling and portaging, though, depending on the situation, as there was no choice being so deep down in this gorge.  the portages were kinda sketchy, and most of us portaged a stretch near the end.  finally back at camp, we looked at it again and made ____ have it checked out at the hospital.  six hour round trip and a bunch of percocets later he was deemed to be ok.

except that the bruising kicked in and the whole area turned black and blue beginning the next day.  then his dick turned black.  purely for medical curiousity, of course we had to see it and he pulls it out and sure enough it was a black dick.  we started calling that rapid "black dick", and it became a great reference point for the creek.  as in, "no, gareth swam just above black dick", or "that entrance drop to black dick sure was tricky", etc.

it was hilarious to us, of course, and provided some levity after nearly seeing him eat it on that creek.  another incident further down (i.e. -- "below black dick") proved even scarier for another fella, but that's another story and no good name came of it.