Alan, this reminds me of the rivers back in Wales, beautiful. I have watched many Atlantic Salmon move up falls like this and they an do it way better than Sea Trout due to the stiff wrist in the tail, it does not collapse, a trouts will.
As a matter of interest how far is that falls from the confluence with the salt.
As a rule ST run into the river at the same time, spawn and return to the Ocean, unlike Atlantics that an remain in freshwater for months before they spawn.
Wales has some great Sea Trout rivers and that fish became a passion of mine.
They are way more wary than a resident river Brownie no doubt of that and way more difficult to catch, particularly during day light hours.
We would fish during the night to catch these fish.
During the day they hide, at night they move into the tails of the pools of where there is well oxygenated water and there you have a very good chance to hook them.
Never cause your shadow to fall on the water, that's a no, no.
Some nights they will hit surface fished flies big time, others no interest, wet flies an be killer for these guys.