Sometimes you actually see fresh water layers (see with your eyes, not a CTD or some other instrument) floating on top of denser waters, not only in your kitchen and with the help of dye, but for real. In this case, you see the layers because the shadow of a pole appears twice — once on the surface itself, and once on the interface between the layers.
See below: Shadow on the surface between the red lines, on the interface between green lines, and the reflection on the surface between blue lines.
I took these pictures on a trip to Husum with my sister and her family.
The other day I went on a trip to Husum with my sister and her family. While walking along the sea, we saw the weirdest thing: Birch trees growing in the middle of the water! From their positions it was clear that they were some kind of marker for the waterway, but it looked very strange. But google suggests that this kind of marker is very common in wadden seas, where the water is too shallow for traditional buoys.
When coming from the sea, you’ll see the birch trees on the port side of the waterway, and on the starboard side there will be poles with branches which are tied together on the very top of the pole, branching out below. Apparently this is called “Pricke” in german. You live and learn! :-)