I travelled to the River at around noon. As expected and hoped for, there was a Dipper by the nest when I got there.  I slid under the cover without the bird which was the male, again as I expected, being none the wiser.  I sat and watched him for a few minutes, he flew up to the nest carrying an insect.  I am pretty sure that he was feeding the sitting female who by now should have been sitting on a nice clutch of 4 eggs. He was noisy as he delivered his morsel to her. Exactly 30 minutes later he was back to bring her more food which he did in the same noisy fashion.  Then around 30 minutes later he flew up to her again and I could clearly see that he was carrying food still as he emerged  again, this time he flew back down still with the insect.  This intrigued me at first but then I saw the female feeding in the shallows just upstream. He obviously thought she was in the nest the same as I! After just a short while she went up in to the nest and he displayed to her as she went in leaving him alone again on the rock.  Later on in the afternoon after I had watched the Wagtails further upstream  I returned to watch again and saw her emerge again, both birds flew off upstream and I guessed that they would be away for at least a few minutes giving me the opportunity to check the nest and confirm that yes, she has got 4 eggs now.  I quickly went back "under cover" and waited to see her return to the nest which she did, everything is going just perfectly.