Gold mining is a significant threat to nearby aquatic species. The initial stage of artisanal gold mining in the western Amazon generally requires the complete removal of all nearby vegetation. This results in an increase in the amount of water that is discharged into nearby streams and rivers.  When local vegetation is removed, turbidity, the haziness of water which depends on the amount of suspended solids, generally increases as well.
This cloudiness and quantity of the water affects the ability of aquatic organisms to navigate and feed properly. In addition, when local vegetation is removed, the mix of fish species present in nearby streams can change. With less vegetation, insect populations decline, and the fish that inhabit the resulting streams are no longer insectivorous, rather, they feed on periphyton, a combination of algae and microbes.  This can, in turn, affect larger species in the environment.
Protecting Amazonian rivers are not solely important for protecting aquatic species. Many organisms require protein that comes from aquatic species in the Amazon such as the terrestrial cats and many species of birds. Humans also depend on freshwater systems for a major source of protein. For many population centers and indigenous territories, fish are the only protein that is readily available. The alteration of watersheds and the species that live in them can therefore cause an economic collapse of the nearby area.  Large scale dam projects have been documented to cause a collapse of fish stock and a problem for nearby human populations. 
Conservation efforts to keep aquatic systems in the Amazon preserved hinge on the careful monitoring of illicit and unregulated gold mining and the development of infrastructure projects that have been approved by biologists in order to minimize their effects. Most importantly, gaps in protection of the headwaters of the Amazon, mountain tributaries in the Andes, must be secured in order to minimize downstream effects. 
Written by Dr. Dave Lutz for the Amazon Aid Foundation
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2.) Holmlund, C.M. and Hammer, M. 1999. Ecosystem services generated by ?sh populations. Ecological Economics 29, 253–268
3.) La Rovere, E.L., Mendes, F.E., 2000. WCD Case Study: Tucurui´ Hydropower Complex, Brazil. Prepared for the World Commission on Dams Secretariat.