Two pairs of tufted ducks were swimming together on West Park lake. Every time I tried to take a picture, one or other of the pairs dived, leaving a ring-shaped wave where they had been. In several shots, the nearest I managed to the complete group was three birds, and the ripple where the fourth had submerged.
I gave up, and went for pictures of the individual birds instead. This time there were no problems of them disappearing underwater.