Hey Nova,
There's a bunch of invisible particle mist generating blocks below the waterfalls on either side of Puea that didn't get set phantom along with the waterfalls themselves and are still preventing passage.
On an unrelated note, there's a lot of little protected parcels around these waterfalls that are like 64m and such that seem to have been carved out when more room was needed for the waterfalls, but weren't joined to the main body of protected land. They also boast of being 2048m. Silly little parcels.