In Southern Australia many ...

In Southern Australia many Waste Water Treatment Plants (WWTP) disposed waste water to rivers and streams.  Such systems relied upon dilution and ultraviolent radiation for purification.  Such practices were leading to problems with blue-green algae and stomach complaints during periods of low flow.  Now- a-days most WWTP now dispose water and nutrients to land in these areas.  This is essentially waste water disposed to pasture in an irrigation system that is used for agriculture.  When loadings and harvesting are designed correctly, nutrients, salt and other 'criteria' are removed  during the agricultural component to provide an ecosystem that is self sustaining into the longer term and there is no need to apply fertilizer in any quantity.