Now this is a bit of a weird story. During summer 2016 to surprise of many, these for 4 pieces appeared ot this old concrete factory. Made during daylight, but nobody really knew who made this. Only a year later is became clear that it was made by artist Johan Opstaele (º1954) who lives on a ship nearby. He wanted to create something at a tolerated place... eventhough this is not really an official graffiti zone. But hey, who cares.

They might look like letters, but they are his own non-alphabet. The color (and title) refers to the water of course. 
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Update: sadly demolished early 2021.