So, I was up on foxton last night when the sheriff came by to advise us that the river was closed--we were leaving anyway, and I didn't want to challenge him about navigable waterways, worthy watercraft, etc., etc., and he seemed very nice--and it sounds like the OP addresses those issues.
There is some damage to the road in isolated areas, so closure could certainly be justified--but it's not impassable, so any justification would be a bit of stretch.
Unfortunately though, a road closure, which was also in effect last night, in this case, is a de facto river closure since you can't set shuttle
The intent of road closure work is always to get the work done and the road opened again asap of course--however it could potentially be closed except for local traffic only--which again would be a de facto river closure
And there's definitely a whole lot more authority and latitude over road closures for state and county officials.
I don't know if the road closure is still in effect, but do any access experts have any thoughts on combatting de facto river closures by closing roads, especially when the closure isn't truly justified?