Alberta River Water Quality Index


An index, whether it is for water quality, air quality or the stock market, is a mathematical way of combining a number of variables into one easily understood value. The Alberta River Water Quality Index was developed specifically as a way to summarize physical, chemical and biological data into a simple descriptor of water quality. The Index provides a snapshot of annual water quality conditions in major rivers of the province

Alberta Environment and Parks (AEP) monitors surface water quality at many river and lake locations each year, but only data collected as part of the province's Long-term River Network are currently used for the Index. Index values are calculated annually for each site based on data collected monthly or quarterly from April to March. Sites are chosen to represent water quality conditions up- and downstream of areas of significant human activity.


The Alberta River Water Quality Index is based on the average of four sub-indices calculated annually for four variable groups:

  • Bacteria (2 variables measured monthly)
  • Metals (up to 22 variables measured quarterly)
  • Nutrients (6 variables measured monthly)
  • Pesticides (17 variables measured 4 times during open-water season)

Variables in the first three groups are compared to Alberta and federal water quality guidelines. Variables in the fourth group (pesticides) are evaluated based on if they can be detected in a water sample. This conservative approach was adopted because some pesticides do not yet have official guidelines and, unlike metals, nutrients and bacteria, pesticides do not occur naturally in the environment.

Following are the variables used in the River Water Quality Index:

Metals & Ions
Aluminum Copper Molybdenum Vanadium
Arsenic Iron Nickel Zinc
Beryllium Lead Selenium Cyanide
Boron Lithium Silver Fluoride
Cadmium Manganese Thallium
Cobalt Mercury Uranium
2,4-D Picloram Bromoxynil Chlorpyrifos
MCPP Dicamba Cyanazine Imazamethabenz
MCPA Triallate Malathion Diuron
Diazinon Atrazine Methoxychlor Dichlorprop
Nutrients & Related Variables
Dissolved Oxygen Total Phosphorus Nitrite-Nitrogen (NO2-N)
pH Total Nitrogen Ammonia Nitrogen
Fecal Coliforms Escherichia coli

View objectives used in the Index calculation:

The formula used to calculate the individual sub-indices is the same as that used for the Canadian Council of Ministers of the Environment Water Quality Index. However, the method for compiling the overall Index is tailored to Alberta.

The Index formula is based on three aspects of water quality that relate to water quality objectives:

  • Scope (F1) - how many variables do not meet objectives?
  • Frequency (F2) - how frequently do measurements not meet objectives?
  • Amplitude (F3) - by how much do measurements not meet objectives?

Rating System

Index results are reported as a number between 0 and 100, where 100 represents the best quality, relative to objectives. The numbers are further ranked into five categories:

96 - 100

Excellent - Guidelines almost always met; best quality

81 - 95

Good - Guidelines occasionally exceeded, but usually by small amounts; threat to quality is minimal

66 - 80

Fair - Guidelines sometimes exceeded by moderate amounts; quality occasionally departs from desirable levels

46 - 65

Marginal - Guidelines often exceeded, sometimes by large amounts; quality is threatened, often departing from desirable levels

0 - 45

Poor - Guidelines almost always exceeded by large amounts; quality is impaired and well below desirable levels; worst quality

Index values are calculated for the four variable groups (metals, nutrients, pesticides and bacteria). These are then averaged, as in the following example, to produce an overall River Water Quality Index:





Overall Index

83 Good

63 Marginal

76 Fair

42 Poor


66 Fair

What Does the Index Show?

Water quality varies naturally from site to site and from year to year. For example, water quality may appear better in drier years, since dry conditions cause less surface runoff and fewer contaminants coming from the land to the river. However, most persistent trends can be linked to human influence.

Any activity that alters water quantity or affects inputs from point sources (e.g., sewage outfalls) or non-point sources (e.g., agricultural runoff) has the potential to influence water quality. In the past, upgraded municipal wastewater treatment has improved water quality downstream of major cities, such as Lethbridge, Calgary, Red Deer and Edmonton; the Bacterial sub-Index reflects this improvement.

How is the Index Used?

Index results are used to evaluate the general quality of river water with respect to four groups of variables: metals, nutrients, bacteria and pesticides. River water quality is reported because the effects of human activities are often more evident in rivers than they are in lakes.

A number of natural and human factors can influence Index values. These include the volume of river flow, local geology, climatic conditions, the degree of development along rivers, non-point sources of runoff (such as agricultural fields) and point sources of effluent that discharge into rivers. These factors are considered in the protection of water quality and aquatic ecosystems as part of the watershed approach outlined in Alberta's Water for Life Strategy.

Using the watershed approach, continuous improvements to river water quality are achieved through upgrades to municipal wastewater treatment facilities and infrastructure, and evolving land use practices. However, such enhancements can be offset by expanding human populations, intensified agricultural activity and expanding industrial development, combined with potentially lower river flows. Over time, the River Water Quality Index should reflect the impact of activities that significantly change water quantity or cause changes in inputs to rivers from either point or non-point sources.

The following document presents a brief history of the Alberta River Water Quality Index reporting from 1996 to present:

Frequently Asked Questions

Screen-reader users: the following section uses links to control collapsible areas of content.

Which Index variables are most likely to not meet guidelines in surface water? What are the potential health effects of these variables?

The variables most likely to not meet guidelines are fecal coliform bacteria, phosphorus and nitrogen. Fecal coliform bacteria may indicate potential health risks to swimmers and may affect crop irrigation and livestock watering. Phosphorus is an important nutrient for plant growth but, if present in high concentrations, can also be responsible for the unsightly growth of nuisance algae and rooted aquatic plants.

Total nitrogen, which includes ammonia, can also promote algal growth. In large quantities, however, it can be toxic to aquatic life and may render water unsuitable for livestock consumption and plant irrigation. Guidelines for these three variables are met more frequently upstream of developed areas than they are downstream.

Compliance with the total phosphorus guideline varies from year to year at all sites. Upgrades to wastewater treatment facilities in major centers such as Lethbridge, Calgary, Red Deer and Edmonton have helped decrease the total phosphorus downstream of these cities.

For example, since Calgary's wastewater treatment plants began reducing phosphorus in their effluent in the 1980s, a noticeable change in phosphorus compliance has been seen in the Bow River downstream of Calgary. This guideline is currently exceeded far less frequently below Calgary than it was in the past.

Annual compliance with the total nitrogen guideline also varies naturally but is generally lower downstream of major centres. The total nitrogen guideline is almost always met in the North Saskatchewan and Bow rivers, upstream of Edmonton and Calgary.

Recent and planned upgrades to wastewater treatment facilities in a number of Alberta cities, including Grande Prairie, will help improve guideline compliance at downstream sites.

Numbers of fecal coliform bacteria almost always meet guidelines at sites upstream of Edmonton and Calgary. Downstream of these cities, the guideline value was often exceeded in the past. In more recent years, Calgary and Edmonton began to disinfect their wastewater with ultraviolet light.

This resulted in improved compliance with the fecal coliform guidelines, as illustrated by the bacterial sub-index. Lower bacterial ratings downstream of Edmonton over the past four to five years appear to be driven by a variety of factors and are currently under investigation by AEP.

Some water quality test results that do not meet relevant guidelines may reflect the impact of natural influences on water quality. During spring runoff, levels of nutrients and metals may exceed guidelines simply because these substances are present in soil and sediment washed into the river.

Which of the rivers identified in the Index have shown the most improvement or degradation? Why?

The River Water Quality Index has been calculated for data from April 1995 through March 2016. At most sites, overall index values reveal no clear tendency toward improvement or degradation.

The majority of year-to-year differences are likely the result of natural variation in runoff and river flows. However, the addition of ultraviolet disinfection to Calgary's Fish Creek wastewater treatment plant in 1997 were reflected in improved bacterial sub-index values for 1997 to 2005 in the Bow River downstream of Calgary.

Similarly, an upgrade to Edmonton's Gold Bar wastewater treatment facility in 1998 led to higher Index ratings for the North Saskatchewan River in subsequent years. More recent declines in the bacterial sub-index downstream of Edmonton, Red Deer, and Calgary appear to be linked to precipitation events and non-point source runoff.

River Water Quality Index ratings for the 2015-16 reporting period were similar to the previous (2014-15) period, with all but three of the 28 monitoring stations achieving ratings of good to excellent.

A rating of fair was observed on three rivers, including the Battle River (one site), Red Deer River (one site), and the Elbow River (one site).

Flows in the Battle River are typically very low, which provides limited dilution capacity. As a result of this and fairly intensive agricultural activity in the basin, the system tends to experience water quality guideline exceedances for nutrients, pesticides and bacteria. Hence, the downstream monitoring station on the Battle River typically achieves a Water Quality Index rating of fair.

The Red Deer River near Jenner received a rating of ‘marginal’ in 2015-16. A significant rainfall runoff event in August resulted in large exceedances of nutrients, bacteria and pesticides as well as several other exceedances throughout the year.

The Elbow River site received a rating of ‘fair’ in 2015-16 due to consistent exceedances of the bacteria guidelines as well as pesticide detections.

In contrast, the Wapiti River upstream of the confluence with the Smoky River received a rating of ‘good’ following two consecutive ‘fair’ readings. This rating was due to fewer exceedances of bacteria guidelines.

Why do Index results not show historical data before 1995?

An overall index value cannot be calculated for data prior to 1995, since pesticides were not part of the sampling program at that time. The index was revised in 2000 to incorporate more variables. Changes to guidelines are incorporated and then applied to all previous years in order to remain comparable.

Trends over a longer time period must be statistically evaluated for individual water quality variables. Surface water quality management frameworks, which have been developed for the Lower Athabasca Region and the South Saskatchewan Region (Bow, Oldman, South Saskatchewan and Milk rivers) assess individual water quality variables and include trend analysis as part of the assessment.

Some sites are reported as having 'excellent' water quality. Is it safe to drink this or any other surface water?

The Index refers to the condition of untreated surface water. Surface water should never be consumed without first being treated. Even so-called ‘pristine’ water can contain pathogens (microorganisms such as Giardia, Cryptosporidium, etc.) that may cause illness in humans.

The source of these organisms is fecal matter from domestic and wild animals, as well as humans. Freezing will not kill these organisms. Any raw surface water can be contaminated and must undergo chemically-assisted filtration and disinfection as a minimum treatment for Alberta municipal waterworks systems.

Why is the Index reported for a fiscal year (March to April), rather than for a calendar year and why is it always more than a year old?

Because of the lengthy and complex process of sample collection, chemical analysis, data entry, Index calculation, and subsequent auditing, the Index can never be completely up-to-date and aligned with all government reporting. A fiscal year presentation allows us to be more current (i.e., 2005-06 data in 2007). The fiscal year also approximates a 'water year' (starting in Spring).

How does the Alberta River Water Quality Index differ from other water quality indices used in the province? Can numbers calculated for various water quality indices be compared?

A water quality index is simply a method for combining complex water quality data into a single number or statement. The index does not replace the conventional scientific process of analyzing and interpreting technical data.

Alberta has made a significant contribution to the development of a Canadian Water Quality Index through its continued participation in a national technical sub-committee under the direction of the Canadian Council of Ministers of the Environment (CCME). However, the CCME Index generally includes fewer variables and no sub-indices as many provinces do not have as broad a monitoring suite as Alberta.

The Canadian Water Quality Index has been officially identified by the National Round Table on Environment and the Economy as an indicator of freshwater quality, and the concept has already been applied in Alberta for a number of different purposes.

These applications all use the same mathematical formula (calculation of scope, frequency and amplitude) but differ in the monitoring programs that support them, the variables and objectives they use, the format they are presented in and their specific purpose.

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Updated: May 29, 2018