This reminds me of the grain of Yew wood, but in fact it's water.
There had been a very heavy rain storm, and the water coming out of the springs in the Well Pool was so silty & orange. The shot was taken where the water flows into the race to the Moat. There was so much water it was tumbling over itself. The darker strip is the distorted reflection of the Main Tower of the Cathedral.
Shot on film.