I'm not sure how accurate the GPS was under the trees there, but you need to take a few steps directly away from the stream from the high point between the two cascades. You are looking for a camoflage container acquired at the Auckland Mega in 2013.
Please ensure that the lid is VERY FIRMLY clicked back on afterwards.
Piwakawaka is the Māori name for a fantail, the small but large tailed, bird that will flit about you in the New Zealand bush, trying to catch the flying insects that you stir up.