[pvaldes]

Russia is implicit in this list, but we need more data. Could be a boycott to keep the current government occupied and not focused on Ucranie or to promote their demise, but could have a simpler explanation also. By now the main categories are industrial dumping or foreign boycott. I don't believe in the climate change/bad luck theory.

The presence of salts is particularly interesting in its three possible ways to end there. Either:

1) Salt was dumped directly in the river by criminals or ...

2) Salt was a by-product of the toxic interacting with the river (Who has access to a lot o mercury salts? We have chemistry experts in HN, maybe some of them could enlight us about some possible chemical paths that release mercury and salt?) or ...

3) Salt (Iodine??) was a second dump aiming to fix the disaster and neutralize the poison after the fishes were killed. Maybe by the government, maybe by the perpetrators.

Many fishes can stand salt for hours or days using their liver to detox, time enough to quit the area. We used salt and freshwater baths routinely to treat our ill freshwater and marine fishes. If is progressive they survive. Carps can stand low quality waters.

The parasites could provide an answer. I would suggest to take a look to them.