Water Quality Parameters

Each station measures the following water quality characteristics or parameters:

What does each water quality measurement mean, and why are these measurements important?

Water temperature is one of the critical parameters that is used to assess our river/stream for aquatic habitats’ health. Many organisms, especially fish, are sensitive to temperature changes in the river water. Fish can be classified into 3 categories based on their sensitivity to water temperature (cold water, mixed water and warm water). For example, Brook Trout found in Orangeville are classified as cold water fish, and are usually an indicator of a healthy river.

Each species of fish has an optimum or preferred water temperature. Fish can sense very small changes in temperature, and when temperatures exceed their optimum by 1-3°C, they are forced to move elsewhere in the stream. If the water temperature shifts too far from the optimum, the fish suffers. Some fish are more tolerant of changes in temperature, since they can survive in a greater range of optimum temperatures. The varied acceptance levels of different fish results in competition between fish that are more tolerant, as they are often more abundant in areas with harsher temperatures. For example, the invasive (non-native) carp species can tolerate temperatures much warmer than 36°C, where other species (like Brook Trout) cannot survive in these warm temperatures. This allows the invasive carp to overtake entire aquatic habitats and prevent native fish from living there.

Water temperature varies daily, seasonally, and annually. Water temperature does not change as fast as air temperature (Figure 1), but because of this, smaller increases in water temperatures can have more of a negative impact on the water quality and ecosystems that depend on this water.

Water temperature has become an important indicator especially in light of climate changes that impact our ecosystems.

Figure 3: Air and water temperature (°C) at the Cooksville Creek at King St. real-time station from December to July 2011.


Turbidity of water is a measurement of the clarity of water that is affected by the presence of solids, small particles/sediments, or pollutants. The more sediments in the water, the more turbid the water is; so our drinking water is low in turbidity compared to water in the Great Lakes (Figure 4)

Fish in turbid water (left), and fish in clear water (right)

Material that is suspended in water allows less light to pass through the water, and so this increases the temperature of the water because the suspended particles hold more heat. Because warm water holds less dissolved oxygen than cold water, the concentration of dissolved oxygen becomes reduced and this affects the fish and other water organisms that need oxygen to live. As such, suspended particles can clog fish gills, that results in reduced resistance to disease, decreased growth rates, and affects egg and fish larval development. As particles settle, they can blanket the stream bottom and smother fish eggs and benthic macroinvertebrates (aquatic insects). Sources of increased turbidity include soil erosion, wastewater discharge, urban runoff (rain water flowing from paved surfaces into waterways), eroding stream banks, and excessive algae growth.

Turbidity can be useful as an indicator of the effects of runoff from construction, agricultural practices, logging activities, stormwater, and wastewater discharges. Turbidity often increases sharply during a rainfall, especially in developed neighbourhoods (or urbanized watersheds) that have relatively more paved surfaces than rural neighbourhoods. The flow of stormwater runoff from paved surfaces rapidly increases the erosion rates of stream banks and river channels. Turbidity can also rise sharply during dry weather if earth-disturbing activities (i.e. during construction) are occurring in or near a stream that does not have erosion control practices in place.

For example, the graph below of turbidity and water level at the Cooksville Creek real-time station displays a sharp increase in turbidity (orange line) on November 28 2011, although there was no precipitation or a large increase in water level (blue line) recorded. On this date, CVC’s Real-time Water Quality Station on Cooksville Creek started sending out alarms due to high turbidity.  CVC staff went to investigate and observed very high turbidity levels in Cooksville Creek and called the Ministry of the Environment (MOE) Spills Actions Center.  CVC Staff then traced the spill upstream to the outfall between Mississauga Valley Boulevard and Kirwin Ave next to the railroad crossing (Figure 6).  The Spills Action Centre was later able to determine that the spill was attributed to a water main break in the Lolita Gardens Neighbourhood.

Figure 5: Water level (m) and turbidity (NTU) fluctuations at Cooksville Creek real-time station.

Figure 6: Cooksville Creek Outfall at rail tracks where spill occurred on Nov 28, 2011


Figure 7: Cooksville Creek under clear (top) and highly turbid conditions (bottom), following a spill event.

Regular monitoring of turbidity can help detect trends that might indicate increasing erosion in developing watersheds. However, turbidity is closely related to stream flow and velocity and should be linked to these factors.

Dissolved Oxygen:

Dissolved oxygen (DO) is a measure of the amount of oxygen dissolved in the water (percent or milligrams of oxygen per litre of water).

Aquatic insects and fish that live in streams need sufficient dissolved oxygen to survive and thrive. Stream waters gain oxygen from the atmosphere and from plants as a result of photosynthesis (the process by which plants turn the energy from the sun into carbon dioxide and water to make food). Microorganisms consume oxygen during the breakdown of organic material from both natural and man-made sources. The amount of dissolved oxygen in the river water can be affected by a range or factors and processes going on in the river.

If more oxygen is consumed than is added or produced, dissolved oxygen levels decline and some sensitive aquatic animals may move away, weaken or die.

Dissolved oxygen levels fluctuate seasonally and over a 24-hour period. Oxygen levels are usually lowest just before sunrise and highest sometime in midday (Figure 8). Aquatic plants can influence dissolved oxygen levels in water as plants produce dissolved oxygen during the daytime and consume dissolved oxygen overnight (photosynthesis).

The levels also vary with water temperature. Cold water holds more oxygen than warm water. The discharge of warm water to a stream raises the water temperature and lowers the oxygen content (see graph below). Aquatic organisms exposed to low dissolved oxygen concentrations may be more susceptible to adverse effects of other stressors such as disease and toxic substances. An hourly profile of dissolved oxygen levels at a sampling site is a valuable set of data because it shows the change in the dissolved oxygen levels from the low point just before sunrise to the high point sometime in the midday.

Figure 8: Diurnal fluctuations of dissolved oxygen (mg/L) with temperature (°C) at the Credit River at Old Derry Rd. real-time station.


pH level is a measurement of the acidity or alkalinity of water. Level of pH can indicate chemical changes in water, and the biological availability of nutrients in water. The pH scale ranges from 0 to 14.

A safe level of pH of water ranges between 6.5 and 8.5 units. pH levels higher than 8.5 become highly basic, while pH levels below 6.5 become highly acidic for water quality.

The pH values in the stream water change due to human activities or due to submerged plants and animals. The effluent discharges that come from industry, stormwater and wastewater treatment plants and quarries may have higher or lower pH levels that in turn change the pH of the stream water.

High acidity or alkalinity deteriorates water quality for both aquatic and recreational purposes and may cause irritation or damage to skin or eyes. Prolonged exposure of aquatic species to higher or lower pH may some times have fatal consequences.


Chlorides are salts often present in areas of urban development. Chlorides in water usually occur as a result of the use of water softeners, road salt, and drainage of swimming pools. The majority of the time, many creeks and streams display chloride levels above the Draft Canadian Water Quality Guideline (128 mg/L).

Levels of chloride in streams and rivers will decrease after a rain event with increasing water levels (below figure).

Figure 9: Summer-time chloride concentration (mg/L) in relation to water level (m) at the Cooksville Creek at King St. real-time station.

During winter months, levels of chloride can be quite high due to the salting of roads and parking lots. Past monitoring of chloride levels from parking lots indicated concentrations of salt over 3 times the salt levels found to occur in oceans! During the summer, chloride level peaks have been observed on weekends when pools are drained and cleaned. High levels of chloride are detrimental to the health of fish.


Conductivity is a measure of the ability of water to pass an electrical current.

Conductivity is useful as a general measure of stream water quality. Each stream tends to have a relatively constant range of conductivity that, once established, can be used as a baseline for comparison with regular conductivity measurements. Significant changes in conductivity can be an indicator that a discharge has occurred or some other source of pollution has entered a stream.

Water Level:

As concentrations of many water quality parameters are related to and dependent on the water levels in the creeks and streams, simply the measurement of water level at each of the real-time stations is essential to interpret what is happening at each of the sites. Real-time information about the water level at each site allows us to determine when a rain event has occurred, as well as how high and how fast the water level increases during a storm. This information may also be useful for flood forecasting and warnings during large storms.

The figure below (Figure 10) displays the increase in water level with precipitation, with larger precipitation events resulting in greater increases in water level.

Figure 10: Changes in water level (m) with precipitation events (mm) in the Credit River at the Mississauga Golf and Country Club real-time station.

COVID-19 related service changes
Data and information released from Credit Valley Conservation (CVC) are provided on an 'AS IS' basis, without warranty of any kind, including without limitation the warranties of merchantability, fitness for a particular purpose and non-infringement.

Availability of this data and information does not constitute scientific publication. Data and/or information may contain errors or be incomplete. CVC and its employees make no representation or warranty, express or implied, including without limitation any warranties of merchantability or fitness for a particular purpose or warranties as to the identity or ownership of data or information, the quality, accuracy or completeness of data or information, or that the use of such data or information will not infringe any patent, intellectual property or proprietary rights of any party. CVC shall not be liable for any claim for any loss, harm, illness or other damage or injury arising from access to or use of data or information, including without limitation any direct, indirect, incidental, exemplary, special or consequential damages, even if advised of the possibility of such damages.

In accordance with scientific standards, appropriate acknowledgment of CVC should be made in any publications or other disclosures concerning data or information made available by CVC.