I wouldn't be concerned about it.

It's getting late enough in the summer; trees are beginning to shut down.

And in most colder zones, messing with the roots at this time of year, can accelerate the process.

Keep it moist but not waterlogged. Water requirements at this time of year are also diminishing. Just don't let it dry out completely being it's a new planting.

Looks nice!

^^ That makes me feel reassured. It's just that it's going downhill so fast, it isn't a gradual decline. The redbud I planted the same day hardly missed a beat, just a smidge of droopiness but nothing concerning.

Transplant shock can vary between different types of trees and methods of transplanting.

I know nothing about redbuds.

If your river birch is dying for some unknown reason, there's nothing you're going be able to do abount it. Drowning a tree with water is never the answer.

Check with your nursery to see if there is a warranty on it and ask their opinion about it.

"Check with your nursery to see if there is a warranty on it."

Yes, one-year warranty.

So they you're covered just in case.

What did your nursery say about your river birch, when you asked them?

"What did your nursery say about your river birch, when you asked them?"

I didn't ask them anything. I've planted river birch before and never had a lick of trouble with them so this is a mystery to me. This is an long-standing, reputable local nursery -- they stand behind what they sell so I'm not concerned about that, but I planted the thing and want it to thrive.

Well, it's always best to ask your seller first, so you know what advice they have to say about it.

That way, if you've done something wrong, they can advise you what to do differently instead of waiting for the tree to die.

You can save yourself a lot of time and energy that way by not having to remove a dead tree and re-transplanting another.

Just FYI.

I hate it when trees do that. I bet it will be fine next spring if you take good care of it the rest of this summer/fall

If I attempted to transplant a birch in full leaf in the summer (which I wouldn't) drowning the tree with water is exactly what I'd do. Until it recovers and established it is basically the same as cut flower bouquet.

I believe that an unestablished, bought at nursery tree, even a river birch, would not do well if the roots were flooded, cutting off access to oxygen, unless you have very well draining soil.

The OP has not told us what type of soil they have.

If it's a heavy soil, you could essentially drown the tree that way.

What constitutes a transplant? I've always thought of it as being digging from ground and moving to another site. It is a bit surprising to see a healthy container-grown tree react this quickly, but it also looks like you're in a bit of a drought. I'd keep it well watered. A gator bag or slow drip hose might be worthwhile. I'd be more concerned with lack of water rather than too much.

"What constitutes a transplant? I've always thought of it as being digging from ground and moving to another site."

Agree. I planted the tree, I did not transplant it.

"The OP has not told us what type of soil they have."

Soil is very well draining. Old farmland. Not clay. Was dry and compacted but I dug deep and wide and broke it all up, backfilled with primarily native soil with a small amount of fresh topsoil to top things off, as I mentioned.

"...but it also looks like you're in a bit of a drought."

Yes it's been very dry for at least a month now, sporadic bouts of rain but not really any good soakers.