>>315734It's too far from the river to have been from a ship and the factory is old and abandoned. It was a road without any sewage drainage.
Pic is how it looked, that kind of rainbowy colour. They were much smaller thouch, a few millimeters, and not too much variation if I recall right.
The only logical thing I could come up with was some firemen or civil protection training, but then again, why would they do that on a friday, after sunset? Our other theory was a drugs lab, but that's pretty improbable too, I guess.
