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.