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Natural Environment

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Key Findings

  • Ontario Line South (OLS) and Ontario Line West (OLW) are mostly urbanized, with little natural habitat; where present, vegetation is limited to parks, rail corridors and residential backyards. As a result, wildlife habitat and habitat connectivity in OLS and OLW are limited. There are no environmentally significant areas in either OLW or OLS. Similarly, Ontario Line North (OLN) is urbanized but contains natural areas associated with the Don River Valley, which includes the E.T. Seton Park Environmentally Significant Area as well as other designated features and natural heritage planning policy areas, and provides important habitat for wildlife in an urban setting
  • Aquatic habitat is present in OLS and OLN, associated with the Don River. This habitat is characterized by poor water quality and a generally degraded aquatic ecosystem. The Don River provides fish habitat important for migration, feeding and refuge. No critically limiting habitats for fish (e.g., spawning habitat) or critical habitat for aquatic species at risk are present within the Study Area. The fish community is mainly composed of pollution-tolerant species
  • The following species at risk have high or medium potential to occur within the Study Area: Barn Swallow, Bank Swallow, Chimney Swift, Butternut Trees and bat species at risk based on presence of suitable habitat
  • The following species at risk have low potential to occur within the Study Area: Bobolink, Eastern Meadowlark and Blanding’s Turtle due to lack of suitable habitat

Spotlight Case

The photo of the Don Valley River was taken from the Charles H. Hiscott Bridge over the Don River West Branch in OLN. The Don River Valley contains continuous natural vegetation, providing habitat for birds and other wildlife, including both common urban wildlife and a number of regionally and locally rare species. The valley is designated as an Urban River Valley under the Greenbelt Plan, 2017 and contains a number of designated natural and planning policy areas such as the E.T. Seton Park.

image of the Don River Valley

Don River Valley (OLN)


Metrolinx conducted a review of available information and field investigations to establish natural environment existing conditions within the Study Area.

The following aspects of the natural environment were examined:

  • Designated natural areas and planning policy areas
  • Vegetation community and plant inventory
  • Fish and fish habitat
  • Wildlife and wildlife habitat
  • Significant wildlife habitat and species at risk

On August 7, 2020, Metrolinx was issued a socio-economic benefit permit in accordance with the Endangered Species Act, 2007.

Preliminary Potential Impacts & Mitigation Measures for Further Study


Potential Impacts

  • Disturbance or displacement of wildlife
  • Removal of/damage to trees, terrestrial vegetation and wildlife habitat
  • Potential impacts to aquatic/riparian vegetation
  • Potential erosion and sedimentation

Potential Mitigation Measures

  • Sensitive-wildlife timing restrictions for construction activities (e.g., removal of vegetation outside of the breeding bird season)
  • Wildlife exclusion measures will be implemented as required to avoid destruction, injury or interference with wildlife species and their habitat
  • Tree/vegetation removals will be kept to a minimum and limited to within the construction footprint
  • Temporarily disturbed areas will be restored/re-vegetated using non-invasive, preferably native plantings and/or seed mixes
  • Construction activities will maintain buffers established during the design phase to minimize potential impacts to wetlands and waterbodies
  • Erosion and sediment control measures will be implemented


Potential Impacts

  • Maintenance activities may result in disturbance/loss of vegetation and habitat

Potential Mitigation Measures

  • Vegetation removal and habitat disturbance will be kept to a minimum and limited to within the Metrolinx right-of-way

Future Studies

  • Additional ecological land classification surveys and plant inventories to confirm vegetation communities, breeding bird surveys, species-specific surveys and/or updated species at risk habitat screening, significant wildlife habitat assessment and/or detailed fish and fish habitat assessments, as required, and a natural environment impact assessment will be undertaken


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