Bioindicators are organisms and/or biological process whose change in numbers, structure or function point to changes in the integrity or quality of the environment.
Aquatic insects are used to determine the condition of the aquatic ecosystem and comparing the ecosystem with a reference level of good ecological functioning and on causes and effects of the relationships within an ecosystem.
If there is a sense of pollutants in the water then there may be an absence of specific aquatic life in the surrounding area