The amazing mackerel sky was reflecting from the still waters high up on Hobgrumble Gill in Swindale. But I was still able to pick out the circular lens-like distortions on the surface of the water. They were slowly rotating.
The also seemed to come in lines, slowly drifting downstream. Tracing the lines back led to the corner of a rock for each line. I wonder if it is some kind of vortex shedding but I would have thought it would need a much more turbulent and faster flow than on this languid calm evening. I have marked some of the eddies in red on the picture below.
