During my packrafting-hiking traverse across New Zealand’s South Island, I packrafted Lake Rotoiti leaving St. Arnaud and then packrafted the Waiau River, starting at Caroline Creek Bivy, after carrying the boat over Waiau Pass. It’s also possible to paddle the upper Waiau by taking a helicopter to the Henry River confluence or hiking or driving the 4WD track from Lake Tennyson over Maling Pass.
The full trip report for my trip can be found here. For those who like this sort of thing, my essay also includes a full sidebar description of how to do this trip and a GPX/KML GPS track of the exact route I took for your fancy electronic devices. (I highly recommend using Maptoaster with the NZ topo maps on your iPhone and loading my GPS track directly into the app for reference).
I made a few mistakes on this trip. Notably, for the Narrows, it’s safe and easy to paddle just to the start of the Narrows and then hike the bypass road – don’t make the mistake of exiting the river too early, as I did because I was being overcautious. Also, be sure to scout and be prepared and wary at the three small gorges before the Narrows. The first (near Delta Stream) is especially challenging and depending on water conditions. It may be prudent to portage it – though it is certainly possible to paddle through safely with lots of care.