Context

Water of good quality and in appropriate quantities is fundamental to ecosystems, human health and economic performance. In Canada, water is mostly used by households and in industries such as electricity generation, agriculture, manufacturing, petroleum extraction and mining. Every year, tens of billions of cubic metres of water are withdrawn from surface and groundwater sources (Statistics Canada 2003). Intensive and competing water uses can lead to local shortages and compromise water quality (Environment Canada 2004b).

Every day, primary manufacturing and service industries, institutions and households discharge hundreds of different substances, directly or indirectly, into rivers and lakes. At least 100,000 tonnes of toxic pollutants were directly discharged to Canada's surface waters in 2003 (Environment Canada 2005c; Statistics Canada 2005). Some substances, such as ammonia and other nutrients, are released in large quantities; other, more toxic substances, such as mercury, are released in much smaller but nevertheless significant amounts (Environment Canada 2005c; UNEP 2002).

Many more pollutants make their way indirectly to water bodies after being released into the air or onto the land. Aquatic ecosystems receive airborne pollutants transported over long distances, such as sulphur dioxide and nitrogen oxides which cause acidification, heavy metals (e.g., lead and mercury) and organic compounds (e.g., polychlorinated biphenyls [PCBs] and pesticides) (Environment Canada 2001). On land, untreated runoff from agricultural and urban areas also degrades water quality (Harker et al. 2000; Marsalek et al. 2001).

Water quality degradation can affect both aquatic life and human uses of water. For example, higher concentrations of nutrients (e.g., nitrogen or phosphorus) may result in uncontrolled plant growth and reduce the amount of dissolved oxygen available for fish and other aquatic animals. Economic activities such as freshwater fisheries, tourism and agriculture can be undermined by degraded water quality. The indicator presented in this first report focuses on water quality for the protection of aquatic life. It does not assess the quality of water for human consumption.

Water quality is difficult to define and assess for the purpose of reporting nationally because water chemistry is complex and depends on many physical and chemical properties that vary naturally from place to place and over time. These properties can affect the suitability of water for aquatic organisms—which themselves vary from place to place and have varied sensitivities to different substances. Evaluating whether water quality is degraded is further complicated because natural processes such as heavy rain, melting ice and snow, soil erosion, and weathering of bedrock also influence levels of certain substances in water (e.g., nutrients and metal ions). These natural phenomena maintain both the habitat for a wide range of indigenous species and the conditions underlying other ecosystem processes. These processes vary considerably across the country, making for a diverse mix of aquatic ecosystems.

To report on water quality, experts have measured specific substances in water, and compared the observed concentrations against scientifically established thresholds for potential adverse effects. This is the basis of the Water Quality Index (WQI) endorsed by the Canadian Council of Ministers of the Environment¹ (CCME) in 2001 and used in this report to produce the water quality indicator (see Box 4). This Index can be calculated using the results of ongoing water quality monitoring programs managed by federal and provincial governments.

Notes

1. The Canadian Council of Ministers of the Environment brings together the Ministers of the Environment from the federal government and all provincial and territorial governments.