Having seen a jet boat go ripping upstream on a Saturday in July when the river is covered in an inflatable hatch, I'm surprised there haven't been more close calls or injuries.
I'd been in favour of jet boat use on the river with speed restrictions and boundaries that reflect water height, fisheries/environmental impact and safety considerations. For example, running at high speed in June when the water is high, there are no spawning salmon and potential for conflict with other users is low may be OK. Doing the same thing in mid summer or in October is not.