I don't know much about this stuff,,, but this is what I read. Although the water has cleared, the heavy metals settle on the bottom, especially in the pools and calm areas. It gets in the mud, and stays there for years.
The yearly run offs will help flush it, but it takes a very long time for mother nature to clean it up. The further down stream you go, the rivers get slower, calmer and it settles there readily and stays longer.
Incredible a mistake like this would occur with a cleanup effort. The stakes are so high you would expect they had a backup plan, on top of a backup plan for the worse case scenario.
I guess not.
2008 Thor Mandalay Presidio, 400 ISL
RVing since 1974!
Lots of Motorcycles