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Wastewater management

Construction, maintenance, operation and decommissioning of facilities that produce and release wastewater that may contain biological or chemical contaminants or that may be of significantly different temperature from the receiving environment. Examples include residential, industrial, or municipal discharges.


Pathways of Effects diagrams have been developed by Fisheries and Oceans Canada as a tool to communicate potential effects of development proposals on fish and fish habitat and were developed through extensive consultation. It is expected that these diagrams will be updated to describe new activities and stressors as required.

Wastewater management


Change in dissolved oxygen: Adequate concentrations of oxygen dissolved in water are necessary for the life of fish and other aquatic organisms. Dissolved oxygen is affected by a number of different factors, including temperature, biological activity, and turbulence.

Change in nutrient concentrations: Some activities may cause an increase in nutrifying elements such as nitrogen and phosphorus and mineral compounds such as ammonia, nitrates, nitrites, orthophosphates. This leads to 'eutrophication', thick growths of aquatic plants (especially algae) that block light needed by aquatic vegetation, either by clouding the water column or coating the vegetation itself. When the algae die, they settle to the bottom and are consumed by bacteria during the decomposition process. This process consumes oxygen, depleting it from bottom waters. The resulting low dissolved oxygen concentrations drive fish from their preferred habitat and can cause other organisms to die.

Pathogens, disease vectors, exotics: Wastewater management sites can be a mechanism to introduce and transport pathogens and other contaminants into the water system.

Change in water temperature: Water temperature directly affects many of the physical, biological, and chemical characteristics of a waterway. In elevated temperatures, many coldwater fish, such as trout and salmon, could experience reduced reproductive activity or direct mortality, including egg mortality. High temperatures also encourage the microbial breakdown of organic matter, leading to a depletion of dissolved oxygen in the water body.

Change in migration patterns: Dams may affect fish populations by preventing normal migration between feeding, rearing, and spawning areas and excessive flow and high water velocities can create migration barriers.

Change in contaminant concentrations: An increase in concentrations of toxins and pollutants in sediments and waters can breach the range of chemical parameters that support healthy aquatic communities, seriously affecting fish and fish habitat. The ecological effects can range from direct fatality to organisms, alteration of the ecosystem structure through changes in the abundance, composition, and diversity of communities and habitats, and persistence and progressive accumulation in sediments or biological tissues (bioaccumulation, biomagnification). Deformities, alterations in growth, reproductive success, and competitive abilities can result.

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