Contaminants in the aquatic environment can have many types of impacts which may include affects on:

• water quality and the health of fish and other aquatic plants and animals
• sediment quality and the health of sediment dwelling organisms
• the health of terrestrial plants and animals
• the health of humans
• aesthetics such as odour, colour or transparency
• social values such as devaluation of property values, increase in water treatment costs or loss of recreational water uses.

Impact assessments are conducted to assess the potential effects on aquatic ecosystems of discharges or other activities for the purpose of obtaining regulatory approval for project development, plant expansion, process change or to address other concerns. Impact assessments also serve to identify sensitive receptors and to identify where changes in project design are required to mitigate adverse effects.