I was tramping with my brother. we had stayed at a hut over night and left early in the morning to tramp to the next hut, Triangle, in the Ruahine Ranges of New Zealand. Weather was misty and starting to rain. We got to Triangle in good time and started to make our way down the river to the next hut, Iron Gate, about 2 hours down stream. The river was low and crystal clear, and the rain had set in. The going was okay down the river until we had nearly reached Iron Gat hut. There another stream met the river with enough volume to make any river crossings down stream impassable. The river was rising and we were in a fix. Climbing a ridge to get a better view and to see if there was a better place to cross the river, only confirmed that we were cut off from the hut and the river was now brown and far to swollen for us to back track to Triangle hut. We were trapped and it was still raining.With food and supplies but no tent and unable to start a fire because everything was so wet we made the decision the activate the PLB. The rescue helicopter winched us out 2 hours later.