Silly sailor?

The rivulet Gersprenz has about 10cm of water these days. But sitting on the balcony I spotted this sail when I looked towards the rivulet. A sailboat? Not possible! Who could be so silly?

Hm, it was not a silly sailor but a silly viewer (read: me). The house opposite of the street probably has a balcony, and the resident(s) of that part of the building set up a shadow sail. Obviously quite literally.

Once again, it is in the eye of the observer.