Freshwater quality

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What is happening?

This indicator, as a water quality index based on many chemical and physical parameters, assesses surface freshwater quality with respect to protecting aquatic life (e.g., fish, invertebrates and plants). It does not assess the quality of water for human consumption and use. The data available are not sufficient to report national trends for the indicator at this time. The indicator is based on information gathered from 2003 to 2005.

• Freshwater quality for the 359 monitoring sites in southern Canada was rated as “good” or “excellent” at 44% of the sites, “fair” at 33% and “marginal” or “poor” at 23%.

• Freshwater quality measured at 36 monitoring sites in northern Canada was rated as “good” or “excellent” at 56% of the sites, “fair” at 31% and “marginal” or “poor” at 14%.

• Phosphorus, a nutrient mainly derived from human activities and a key driver of the water quality index, is a major concern for surface freshwater quality in Canada. Phosphorus levels in southern Canada exceeded limits set under the water quality guidelines for aquatic life over half the time at 127 of 344 monitoring sites.

Other water quality indicators, information and analysis for drinking water sources, agricultural use and recreational use are being developed as part of the freshwater quality indicator series.

Figure 4 Status of freshwater quality at sites in southern Canada, 2003 to 2005

Why is it important?

Water of sufficient quality and in adequate quantities is fundamental to healthy ecosystems, human health and economic performance. Degradation of water quality can affect both aquatic life and human uses of water. For example, high concentrations of nitrogen and phosphorus in the water may result in excessive aquatic plant growth, such as algal blooms, which reduce the amount of dissolved oxygen available for fish and other aquatic animals. Some algal blooms can also be toxic, killing livestock and resulting in the closure of shellfish growing areas, and represent a human health risk. Degraded water quality can also affect economic activities such as freshwater fisheries, tourism and agriculture, or recreational uses of water such as swimming.

Why is it happening?

Manufacturing and service industries, institutions and households discharge hundreds of different substances, directly or indirectly, into rivers and lakes. At least 115 000 tonnes of pollutants were directly discharged to Canada’s surface waters (both freshwater and coastal) in 2005. Many pollutants also make their way into water bodies indirectly after being released into the air or onto the land. Runoff from agricultural lands and urban areas with high concentrations of nitrogen and phosphorus can also degrade water quality, as can changes to water flows. Natural phenomena such as seasonal snow melt and heavy rainfall can also be responsible for water quality measurements not meeting guidelines; for example, they can increase levels of suspended sediments that are often high in nutrients and metals.