Shoulda posted this here at the same time I posted it to rpd.health:

Orson has cold tail for the first time. It's sad to see him so lethargic,
biting at his tail, and especially so since I believe the cause of his
condition is that I worked him too hard in the water.

But the purpose of my post is something else. I googled on cold tail when I
suspected that's what he had, and I saw lots and lots of posts from people
who assume cold tail is from cold water. (Especially a lot of posts, for
some reason, about people vowing never to take their labs swimming in the
Pacific again.)

But this is late May in Baltimore, where we've had highs in the mid- to
upper-80s for several weeks. The water temp in the Chesapeake Bay, where he
was swimming, has got to be at least 68. Nothing like swimming in upstate
New York in January, which he used to do routinely (and which never gave
him cold tail).

IOW, the water doesn't have to be cold for a dog to get cold tail. Just
thought I might be able to enlighten others on something I didn't know.

Cate