Canadian Water Quality Guidelines for the Protection of Aquatic Life CCME WATER QUALITY INDEX 1.0 User's Manual

Summary A water quality index provides a convenient means of summarizing complex water quality data and facilitating its communication to a general audience. The CCME Water Quality Index (1.0) is based on a formula developed by the British Columbia Ministry of Environment, Lands and Parks and modified by Alberta Environment. The Index incorporates three elements: scope - the number of variables not meeting water quality objectives; frequency - the number of times these objectives are not met; and amplitude - the amount by which the objectives are not met. The index produces a number between 0 (worst water quality) and 100 (best water quality). These numbers are divided into 5 descriptive categories to simplify presentation. The specific variables, objectives, and time period used in the index are not specified and indeed, could vary from region to region, depending on local conditions and issues. It is recommended that at a minimum, four variables sampled at least four times be used in the calculation of index values. It is also expected that the variables and objectives chosen will provide relevant information about a particular site. The index can be used both for tracking changes at one site over time, and for comparisons among sites. If used for the later purpose, care should be taken to ensure that there is a valid basis for comparison. Sites can be compared directly only if the same variables and objectives are used; otherwise, a comparison of the sites’ ability to meet relevant objectives must be made in terms of the category obtained.