The River Itchen runs through the center of Winchester and, just downstream of the old mill building, the water is very shallow.  The river bed provides a good location for a lot of weed to grow and the ducks seemed to enjoy feeding on this weed.  However, it did require a fair amount of effort on their parts as the current was flowing fast in the shallow areas.  It was fun watching them either paddling furiously or bracing against the river bed while dipping their heads under water to feed.  The water would sometimes roll up across their backs while they fought to stay in place.  After watching this for a while, guess what I chose to have for dinner!