Aquatic Habitat and Species

Toronto and Region Conservation monitors fish, 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 Lake Ontario waterfront:

Aquatic Insects

Data on aquatic insects are collected annually from May to November at 150 monitoring stations across the region. Aquatic insects 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.

TRCA monitoring aquatic insects

Members of our 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. For example, 2015 marked the 5th year that fish and habitat monitoring activities were focused on the Duffins, Carruthers, and Rouge river watersheds. In 2016, the focus will shift to the Etobicoke Creek and Humber 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.

TRCA fish habitat and community monitoring

Fish 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. Fish, sediment and aquatic vegetation surveys are also regularly conducted within Toronto Harbour as part of short-term special projects.

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.

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 in 2015 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