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Water Quality

Goals and strategies to protect, improve and manage water quality are identified in TRCA watershed strategies and plans, and the Remedial Action Plan for the Toronto region.

Surface Water Quality

Clean water is an important component of a healthy watershed ecosystem. It helps support diverse aquatic habitat, vibrant recreational areas, good quality drinking water, and adds to our aesthetic appreciation of the natural environment. Goals and strategies to protect, improve and manage water quality are identified in TRCA watershed strategies and plans, and the Remedial Action Plan for the Toronto region. The TRCA, in partnership with watershed councils, member municipalities, and other government agencies, has developed several programs to address issues of water quality, including routine monitoring of stream health, encouraging prevention of pollution at source, management of non-point source pollution in rural and urban areas, implementation of stream restoration projects, promotion of stormwater best management practices and programs designed to raise awareness about the importance of preserving water quality in our rivers and lakes.

Chemical and Physical Conditions

The quality of our streams and lakes is currently monitored through the TRCA's Regional Watershed Monitoring Network. Through the Network, the TRCA partners with the Ontario Ministry of the Environment and the City of Toronto to collect monthly water samples at 27 stations in nine watersheds. Samples are analyzed for a wide range of parameters, including nutrients (phosphorus and nitrogen compounds), metals, bacteria, total suspended solids and other general chemistry parameters. A recent report summarizing results from 1996 to 2001 for the Toronto Area watersheds is available by clicking here - 4,210K pdf icon Water quality data are also interpreted in the context of other watershed studies and assessed in report cards and watershed strategies for individual watersheds.


Biological monitoring, or biomonitoring, uses biological communities, such as fish or benthic invertebrates, to assess environmental conditions. If the monitoring shows an impairment, additional chemical and toxicity testing can help to identify the cause and source. Since biological communities live in receiving waters, their health and survival reflects the integrated effect of chemical, physical and biological influences over extended periods of time. As such, biomonitoring is an important complement to chemical monitoring programs because the latter indicate stream conditions only at times of sampling and, consequently, short term or intermittent shocks associated with chemical spills, stormwater discharges or non-point sources of pollution are not easily detected. Biological indicators used by the TRCA to evaluate stream health include the following:
Young-of-the-Year Fish
Benthic Invertebrates

Rural Water Quality Management

Non-point sources of nutrients and other contaminants to the Great Lakes from agricultural activities and rural development has been a concern for many years. Since pollutant loads from rural areas vary widely and occur over a large area, adequate characterization of the problem through monitoring is not practically feasible. To help overcome this problem, the TRCA is currently using a water quality model designed for rural applications (the Agricultural Non-Point Source Modeling ) to identify priority sources of contaminants in the watersheds. Results will subsequently be used by the Rural Clean Water Program to target remedial programs designed to reduce sources of rural pollution.

Stormwater Pollution Prevention

As a general principle, it is cheaper and more effective to avoid or minimize the creation of pollution than it is to repair damage caused to the environment once it occurs. Control of water pollution through output or end-of-pipe treatment addresses the symptoms of the problem, but not he cause.

A myriad of opportunities exist for businesses, communities, municipalities and citizens to take action in preventing water pollution. To find out more about what you can do, read the Stormwater Pollution Prevention Handbook, a report funded by the TRCA, Ontario Ministry of Environment and Energy and the Government of Canada's Great Lakes Sustainability Fund.

Visual Aesthetics

The visual aesthetic condition of Toronto region streams and the waterfront is highly degraded. Degraded aesthetics are caused by undesirable algae growth, litter and debris, cloudy waters from sediment erosion, unpleasant odours from dumping or spills and unnatural alterations to the watercourse that have occurred over time.

To help quantify the extent of the problem, the TRCA initiated a community-based visual survey in October 2001 and 2002. Members of the community conducted the survey over a section of stream or the waterfront in their neighbourhood. A report presenting and interpreting survey results is available by clicking here - 546K pdf icon and an accompanying here - 1,290K 


Oil and chemical spills occur frequently in TRCA watersheds. Some of these are discharged to the soil, others find their way into rivers either directly as overland runoff or indirectly through the storm sewer network. The impact of these short-term shocks can be devastating to downstream aquatic communities, and in some cases the effects may persist in stream sediments for years after the spill has occurred. The TRCA is currently working with municipalities and other agencies to identify spill locations and spill prone areas, and evaluate preventive and control options. Summaries of study results in selected municipalities can be obtained by clicking here:-Markham[500k] Richmond Hill[553k] and Vaughan[527k]. In future reports, spills data will be compared with routine monitoring data from the Regional Watershed Monitoring Network to help quantify impacts and identify appropriate remedial actions.

Young-of-the-Year Fish :Young-of-the-year, or juvenile fish, is a good indicator of stream health because these fish have a limited geographical range relative to adult fish and tissue analysis of persistent bioaccumulative substances provides an understanding of exposure times. A discussion of young-of-the-year data in the TRCA jurisdiction is provided in TRCA's watershed strategies and report cards.

Algae:Algae are recognized as a good biological indicator of water quality because they are sensitive to water chemistry and their short life cycle allows for early assessment of changes in pollutant loading. A pilot project in the spring of 2000 conducted by Dr. Marianne Douglas and her students at the University of Toronto, and sponsored by the TRCA, showed that diatoms were a useful biomonitoring tool for environmental assessment. A more detailed study is currently underway to monitor periphytic diatoms in the TRCA's watersheds and relate these to water chemistry conditions. Results of this study are expected in the summer of 2004.

Benthic Invertebrates:Invertebrates are insects that live in or on the bottom-sediments of streams and lakes. They are distributed widely, live out their lives in a relatively small area and have widely varying tolerances to physical and chemical conditions. These characteristics make them suitable as an indicator of water quality in receiving waters. Benthic monitoring is conducted through the Regional Watershed Monitoring Network.

FishThe diversity and species of fish populations inhabiting a stream are good indicators of habitat conditions and long-term stream health because they exhibit a range of tolerances to pollutant levels and environmental requirements for most species are well known. For example, cold water fish species, such as brook trout, generally can not tolerate maximum stream water temperature above 21 C, and these species are also relatively intolerant to pollution. In contrast, bottom dwellers are adapted to low oxygen conditions and can usually tolerate higher levels of organic pollution than other species. Thus, in a particular location, the presence of certain species of fish and not others can provide valuable clues about the quality of water at the site.

The TRCA monitors fish species and their habitats throughout the TRCA jurisdiction. Detailed statistics and recommendations for management are contained in Fish Management Plans for each of the watersheds.

Agricultural Non-Point Source Modeling:The AGNPS model is a distributed water quality model, designed to predict water quality and hydrologic response conditions in agricultural watersheds for the purpose of developing and evaluating best management practices. Developed by the U.S. Department of Agriculture, the AGNPS model is an event model, simulating conditions based on a single precipitation event, uniformly distributed across the catchment. The model considers a wide range of factors affecting water quality, including soils, land slope, nutrient and sediment loading, local hydrology, land use practices, precipitation, drainage, erosion and existing water quality. The AGNPS model has been widely tested in the United States and is generally accepted as a useful tool in evaluating the relative impact of different land cover scenarios and Best Management Practices on surface runoff, sediment and nutrient transport (nitrogen and phosphorus) at the watershed scale. A copy of a recent TRCA report on application of the model to the Duffins and Carruthers Creek watershed can be obtained by clicking here - 2,200K

Lake Ontario Ajax and Pickering Nearshore Water Quality

TRCA conducts scientific monitoring of Lake Ontario water quality in the Ajax and Pickering nearshore areas of Durham. The "nearshore" generally includes the shoreline (or lake edge) and the area of the lake out to a depth of approximately 30 metres. Nearshore water quality shows us the effects of activities in the watershed on the lake which receives this water. Activities on land, and in the streams which empty into the lake, also affect the conditions of Ajax and Pickering beaches. TRCA monitors water quality in the proximity of the intake for Durham Region's Ajax Water Supply Plant and near the Duffin Water Pollution Control Plant outfall. Monitoring has been ongoing since 2007. TRCA shares this data with academics, other governments, and the public. Click here to visit the page.