I have never heard of anything that took oxygen out of the top foot of water. It seems to me that doing that would also deprive small fish that inhabit shallows. If such a product exists I would be reluctant to use it.
There are a lot of chemical herbicides that are acceptable and formulated for land use that are not recommended for ponds. Like a lot of things, I think a little bit doesn't really hurt.
If it were me, and it's not, I would go the backhoe route. Admittedly, they make a mess on the shore,
On your last photo I see a lot of lily pads and it looks like something else. Can you get a closer photo and post it?
