The MercuryThe way I understand it is the mercury has always been trapped in the soil for ever and disturbing the soil is what releases it. You can't have open pit mining without disturbing the ground in a certain area. These things were known ahead of time and unfortunatley it's the price of doing business. Diamond processing is by FAR the cleanest as we all know so the question is do the people that hold the land dear to thier hearts accept these things or not, they did for the first Debeers pit, we shall see very soon if they do for the second.
All this being said I have not heard of dead fish or damage to the species in the area, however if the mercury is causing those kinds of things then I would have to say it needs to be dealt with but again I have heard of nothing bad happening, maybe others have, that I don't know.