Thanks so much @NoSI
! Beautiful river photo! It looks even narrower in this photo than what I've seen in others. I wonder what time of year this photo was taken, first guess autumn, but IDK.
I had been thinking that if she was in a container, cooler, barrel, etc. He would have moved rocks to make a hole and then replaced them atop the container in the hole and made sure the rocks covering the area would be heavy enough to not be moved down stream by the current.
He would have made holes in the container so that it would not be able to float and probably added rocks inside for weight. It could have been done and been easier to do) at the edge close to the shore. (Just covering some speculation regarding bodies or skeletal remains floating down the river or it being too rocky). MOO
That being said, I defer to the posters who are familiar with the river and the available river data.
And I still think it more likely (not decidedly) that she is in a container at the bottom of an abandoned mine.