Concentrations of river pollution are monitored regularly by water authorities and the results of their monitoring are available to the public. Monitoring results—used in conjunction with the results of effluent sampling—will help demonstrate where pollution in the river originates and how much impact on river quality the discharges from a particular factory or sewage works are having. However, factories and sewage works are not the only causes of river pollution; other sources also have to be considered when interpreting monitoring results. Similarly, changes in river quality may be caused by variations in natural factors and not by increased or decreased discharges of effluent.
