River Water Quality Index: More about the data

The River Water Quality Index formula is similar to the CCME (Canadian Council of Ministers of the Environment) Water Quality Index, though the method for compiling the index is tailored to Alberta. Based on data collected monthly or quarterly at Long-Term River Network sites, the index is calculated annually as an average of sub-indices for four groups of variables: metals, nutrients, bacteria, and pesticides. Variables in the first three groups are compared to Alberta and Canadian (CCME) water quality guidelines. Variables in the fourth group (pesticides) are evaluated based on whether or not they are detected in a water sample. To see the index data for 2005-2006, including the sub-index values, click here.

Other water quality data is available on-line at http://www3.gov.ab.ca/env/water/reports/water_quality_reports.cfm

Rating System

The River Water Quality Index formula incorporates three factors representing key aspects of water quality. They are: the number of variables not meeting water quality objectives (scope); the number of times objectives are not met (frequency); and the amount by which objectives are not met (amplitude). The result is a number between 0 and 100, where 100 represents the best quality, relative to objectives. The numbers are further divided into 5 categories:

• Excellent (96-100) - Objectives almost always met
• Good (81-95) - Objectives occasionally not met, but usually by small amounts
• Fair (66-80) - Objectives sometimes not met by moderate amounts
• Marginal (46-65) - Objectives often not met, sometimes by large amounts
• Poor (0-45) - Objectives almost always not met by large amounts.