I planted an apple tree this spring, and it was doing fine at first but now it looks really sick (see pictures). I live near Austin, and we've been getting tons of rain lately, and the soil is poorly drained clay. Maybe that's hurting it. I don't know.

What do you think is wrong with it? And what can I do?

I see some of those leaves have turned yellow. Did you happen to notice if it started from the bottom of the tree?
If so it really looks like waterlogged soil.

I don't know if it started from the bottom of the tree. I know the soil is waterlogged. What can I do about it?