I believe it is the second or third set of gates that it is below.
The log starts on river left and runs to the center. It completely blocks the channel that is spans but it not usually a channel that gets run. Stay in the middle of the river (but watch out for some of those holes) and you should be good to go.
Be careful because the Men's US team sometimes moves the gates to the side so you might lose the marker...
That log will be lower at higher water levels because eventually you'll be able to go over it but not it wouldn't be pretty.