It is quite polluted with nitrates etc. but the appearance isn't new if Kipling wrote about it. I've seen it at different times of the year and at different places and there are fish as well as vegetation. It's supposed to be quite silted when flooding so that may be part of the story. Certainly there is mining in parts of the basin, but the area is mineral rich naturally anyway. It's not quite a Parys Mountain run-off.