Significant impacts on water quality of the inner harbour predicted if Billy Bishop Airport expands – City of Toronto report

A June 30, 2026 city report has noted that the proposed Island Airport jet expansion would negatively impact the water quality of the inner harbour as well as reduce the impact of the billions of dollars invested in the Don River and Central Waterfront Project. The concerns are based on the Toronto Port Authority's own 2017 Environmental Assessment related to the introduction of jet aircraft to a much shorter runway extension. A report that was not available to the public until just recently through a Freedom of Information request.

From the report:

Through initial analysis based on information that has been reported in the media about the proposed expansion, and the publicly available documentation related to previous expansion proposals, staff have identified the potential for negative impacts on water quality in Toronto’s Inner Harbour from a proposed BBTCA expansion. Based on available information from the Toronto Port Authority’s 2017 Environmental Billy Bishop Airport Proposed Expansion: Supplemental Report 1 of 7 Assessment, runway extensions may reduce water flow and increase residence time, limiting the harbour’s ability to flush pollutants from the Don River, stormwater outfalls, and combined sewer overflows. These impacts would result from altered circulation patterns, increasing pollutant accumulation, and new contamination risks. This could negatively affect the intended improvements from ongoing multi-billion-dollar City stormwater and wastewater investments through major infrastructure projects.

Toronto’s Inner Harbour sits between downtown Toronto and Toronto Islands and is a shallow basin that receives flow from the Don River. During rain events, the Inner Harbour may also receive flows from storm sewer outfalls and combined sewer overflows (CSOs).

The Toronto Port Authority’s 2017 Environmental Assessment related to the introduction of jet aircraft at BBTCA considered the effect of a potential 200-metre long runway expansion. The study found that the constriction created by the runway expansion would reduce flow through the western channel by approximately 50% and nearly double the residence time of water in the Inner Harbour. The increase in residence time was predicted to have a significant impact on water quality through reduced dilution and flushing of pollutants from the Don River, CSOs and storm sewer outfalls. This issue was addressed in 2026.PH31.5 and is further discussed in this supplemental report.

The City is making multi-billion dollar investments to improve water quality in the Inner Harbour through the Don River and Central Waterfront Project. This project will keep CSOs out of the Inner Harbour, Lower Don River and Taylor Massey Creek. The project as designed is for a wet weather flow system to capture CSOs, transport stormwater to a wastewater treatment plant for treatment, and store CSOs during heavy rainfall until system capacity is restored to allow for treatment. Construction of this project began in 2018. Although there is no available plan for the proposed airport expansion available at this time, a reduction in water quality in the Inner Harbour resulting from BBTCA runway expansion, as contemplated in the 2017 EA, could reduce the positive impact from these investments.

Oversight of lakefill quality

Through media reports, the Province has stated its intent to designate the BBTCA as a Special Economic Zone (SEZ). The SEZ would allow for broad exemptions from Provincial Acts and regulations, including those that restrict the use of contaminated fill material. As such, through the Federal jurisdiction of airports, care must be taken to ensure that any lakefill material used for a potential airport expansion meets environmental standards to avoid significant water quality impacts that would impair the City’s drinking water source and safe recreational use of the lake.

Impact of de-Icing from expanded airport operations

An expansion of operations at BBTCA can be expected to result in more use of de-icing agents and aircraft fuel, increasing the potential risk of chemical spills. BBTCA has an on-site containment system for de-icing runoff that is functioning adequately, but any expansion of the airport would require that this system be reviewed and improved to manage increased loading.

Read the complete report

City report – the proposed Island Airport jet expansion would negatively impact the water quality of the inner harbour