Yay, Poland! I used to live along the Columbia River in the US, and sadly, like so many rivers in the World it is used for an industrial dumping ground. Very murky water, but for one small beach, which was full of clams in the water. There, the water was crystal clear. Not good for swimming, because clams are sharp! They certainly cleaned the water though. We need to let Nature do its job more often.,(reply>), @M. Wisniewski Those will be some busy clams! I think it might be a great solution to a current problem, excuse the puns. 🙂,(reply>), Vistula unfortunately is also a dump - mining industry dumps its waters there. Also there is some municipal sewage dump problem (nowadays mostly due to industrial accidents, but still). That is why water quality monitoring is more important than ever