Aquatic Habitat and Species

Toronto and Region Conservation Authority (TRCA) monitors fish communities, aquatic insects, habitat features and temperatures within local streams as well as in Lake Ontario. TRCA offers a number of technical training workshops related to these topics.
What do we monitor and why?

TRCA monitors the following key indicators to assess the aquatic health of our regional watersheds and the Toronto regional waterfront area in Lake Ontario:


Data on benthos are collected annually from May to November at 150 monitoring stations across the region. A total of 47,880 benthos were collected from 133 RWMP monitoring sites in 2017.  Benthos are useful as water quality indicators because they live within the bottom of streams or rivers for their lifespan (one to three years), and are sensitive to disturbances in the environment. They can include worms, snails, mussels, leeches, crayfish as well as the immature life stages of insects. Their relatively high abundance and the low cost of equipment make them ideal organisms for monitoring.

Members of TRCA’s aquatic monitoring team are provincial leaders in identifying aquatic insects to the Lowest Practical Level, with staff certified in genus level identification by the Society for Freshwater Science. Annually our team offers external training in Ontario Benthos Biomonitoring Network (OBBN) standardized sampling protocols to environmental professionals. OBBN is a multi-sector biomonitoring collaboration led by the Ontario Ministry of the Environment and Energy, whereby members can share their data through a centralized database.

Fish Communities and Habitat

Each of TRCA’s nine watersheds are surveyed for fish communities and habitat features every three years. 2017 marked the sixth year that Regional Watershed Monitoring Program (RWMP) fish and habitat monitoring activities were focused on the Don River, Highland Creek, Mimico Creek, Petticoat Creek and Frenchman’s Bay watersheds.  A total of 1,713 fish records were collected from 39 RWMP sites. In 2018, the monitoring focus will shift to the Duffins Creek, Carruthers Creek, and Rouge River watersheds.

Fish are excellent indicators of stream health because they are easy to collect and identify in the field, are sensitive to changes in their environment, differ in their tolerance to amount and types of pollution and are sensitive to forms of pollution that chemical tests may miss. To help predict what types of fish are likely to be found, in-stream habitat characteristics (e.g. stream widths) and bank assessments are completed together with the fish community surveys.

Coastal fisheries surveys have also been conducted within Toronto Harbour since 1989 in order to track the effectiveness of Remedial Action Plan (RAP) remedial measures for the Toronto & Region Area of Concern (AOC). AOCs are formally recognized by the governments of Canada and the United States in the Great Lakes Water Quality Agreement (GLWQA) amendments of 1987. A total of 19,960 fish records were collected from 112 coastal monitoring sites in 2017. Additional coastal fish and habitat assessments are also regularly conducted within the Toronto area waterfront in support of various habitat restoration projects, environmental assessments and research studies.

TRCA also coordinates Aquatic Habitat Toronto (AHT), a group of agencies that have a vested interest in the improvement of aquatic habitat on the Toronto Waterfront. AHT is focused on completing the goals of the Toronto Waterfront Aquatic Habitat Restoration Strategy and the Fishing In Your Backyard: An Urban Recreational Fisheries Strategy for the Lake Ontario Northwest Waterfront, as well as working with academia on a multi-year fish-tagging study.

Water Temperature

TRCA collects water temperature data using seasonal and year-round temperature loggers. Temperature is a major factor that determines which aquatic species, fish or bugs, live in a particular stream. For example, Brook Trout rely on groundwater upwellings for spawning. Tracking water temperature can also indicate the influence of groundwater on a watercourse. Toronto watersheds are historically dominated by coldwater stream conditions. The more urbanized the surrounding landscape becomes, the higher the water temperatures. This data helps to measure the effects of urbanization and climate change on stream health. In 2017, water temperature data was collected from 104 in-stream monitoring locations plus 54 locations along the Toronto area waterfront.

TRCA aquatic monitoring

West Nile Virus Larvae

Mosquito larvae populations are surveyed through the West Nile Virus Surveillance and Monitoring Program. The data collected are used to identify sites of potential concern or hotspots and then follow up with appropriate management actions. LEARN MORE.

TRCA West Nile Virus monitoring

What are the data telling us?

Data analyses continues to show that streams in urban areas with high road densities are less healthy. This suggests that decreases in urban area and road density, as well as increases in natural cover (e.g. % forest), will maintain or improve the health of our watersheds in the future. This map shows the average health of aquatic habitats and communities across TRCA watersheds.


Healthier sites are generally located in coldwater streams in the upper reaches of the watersheds where there is low levels of urbanization (<10%) and relatively high levels of forest cover (12-40%). Individual monitoring sites in good health are usually located in the Duffins Creek, Rouge River and Humber River watersheds.

Unhealthy sites are typically located in streams surrounded by high levels of urbanization (63-100%) and low levels of forest cover (<2%). These sites also tend to have man-made modifications such as concrete lined channels. Most of the impaired sites are located in the Mimico Creek, Don River and Highland Creek watersheds.


Rick Portiss, Senior Manager
Environmental Monitoring and Data Management