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Data Sources and Methods for the Freshwater Quality Indicator

Description and rationale of the Freshwater Quality Indicator

2.1 Description

The Freshwater Quality Indicator (WQI) provides an overall measure of the ability of freshwater bodies to support aquatic life at selected monitoring stations across Canada. It is a water quality guideline-driven tool used to distill large amounts of water quality data at a monitoring station into a single index. Water quality at a monitoring station is considered excellent when ambient water quality does not exceed guidelines at any time for any of all selected parameters. When water quality is rated poor, water quality measurements usually exceed their guideline; exceedences at these stations may be large.

2.2 Rationale

Clean water is essential to sustain healthy ecosystems and the many benefits they provide us. The WQI provides a national perspective on the overall quality of untreated freshwater for aquatic life in Canada. The WQI assumes that if measured ambient water quality does not exceed its water quality guideline, it is acceptable for aquatic plants and animals. The WQI provides information about the state, and change through time, of surface freshwater quality, in order to help inform water resource management.

2.3 Changes since last report

Since the last report, the water quality guidelines for chloride and nitrate have been updated by the Canadian Council of Ministers of the Environment (CCME). This change resulted in the WQI scores going down at several stations in Ontario where chloride is included in the WQI calculation. It had no impact on British Columbia stations that included chloride in their calculations. No stations changed category because of this update, and the analysis of changes through time is not affected.