The long-term health of our waterways is contingent on the maintenance of a properly functioning ecosystem; one with the ability to support a natural diversity and abundance of biota as well as providing critical functions, such as nutrient cycling. In order to determine whether ecological health is being maintained biotic indices are often employed.
Biotic indices use observations of algae , plants and animals (i.e. fish and macroinvertebrates to determine whether systems are functioning naturally and in a sustainable manner. Biotic indices have the ability to gauge direct toxic effects from contaminants along with indirect effects from changes in water quality or habitat that can come from alterations in land use, removal of fringing vegetation or reduced connectivity (fish barriers), amongst others.
More information can be found on biotic indices in the assessing river health and assessing estuary health sections.