Nickel is generally present in water bodies at varying concentrations depending on the nature of the underlying geology. In river systems, the influence of natural and anthropogenic activities will also influence the ambient concentration of nickel. Where there are industrial activities, the levels of nickel may become more elevated.  Sediments in freshwater and marine systems also contain nickel naturally, and this environmental compartment may act as a sink for nickel in systems that receive anthropogenic sources. 

Nickel may end up in water from both point and non-point sources. Diffuse nickel emissions may stem from sewage treatment plants, power plants, waste incinerators and metal industries and application of sewage sludge to land.  Nickel is directly emitted from a number of industries through direct discharge to surface waters, usually after waste treatment. The emission limits are strictly controlled in regions like Europe and North America. 

Information on nickel aquatic toxicology is extensive, and general patterns have emerged.  For example, the most sensitive aquatic organisms tend to be invertebrate zooplankton, whereas fish are generally more tolerant.  Also, effects of nickel exposure vary greatly among different freshwater systems as a function of differences in water chemistry.  The mechanisms behind these differences are well understood, and are beginning to be used in setting Environmental Quality Standards for nickel.  Further information on water ecotoxicity of nickel can be found here for freshwater and here for the marine aquatic compartment.