@Crow Horse
I do not have a kayak so I can not add anything in the way of under water mounting advice.
However I have and still do record with the GoPro subsurface.
Usually fish release shots.
Clear water is pretty much a must.
Point of interest is, although most all GoPros are rugged and waterproof right out of the box,
I have drown a couple of different units the past few years.
Used them at arms length underwater boat side.
One minute they worked, the next - toast.
So while nothing is fool proof, all my future underwater deals now include
a GoPRO branded waterproof protective housing made for the model cameras I'm using.
Adds an extra layer of protection for H2O intrusion.
https://gopro.com/en/us/shop/mounts-accessories/protective-housing-plus-waterproof-case/ADDIV-001.html
If something like this is available for your unit, I'd recommend considering it.
also You might want to designate a water only camera.
Good Luck
A-Jay