The Ontario government has approved a plan from the Independent Electricity System Operator (IESO) to build a new underwater electricity transmission line from near the Darlington Nuclear Generating Station to the downtown core and eastern portion of the City of Toronto.

“Without a new transmission line, Toronto would have to turn down job-creating investments and reduce housing, which is simply unacceptable,” said Energy Minister Stephen Lecce. “We are thinking ahead and building for the future by approving a new transmission line that will enable 285,000 new homes, power new businesses, and create thousands of jobs. We are also initiating the first IESO-led competitive transmission procurement to reduce costs and maximize benefits for families.”

The City of Toronto is currently supplied by two transmission lines, one from the west at Manby Transmission Station (TS) and one from the east at Leaside TS. These pathways will begin to reach their capacity in the 2030s, demonstrating a clear need for additional transmission infrastructure.

The plan to build a third transmission line will meet growing demand by delivering 900 MW of additional power, equivalent to all the power generated from three small modular reactors, or power for 900,000 new homes.

“Toronto is the fastest-growing city in North America, and that growth means we need more power to fuel our homes, transit, and businesses,” said Mayor Olivia Chow. “I want to applaud the Ontario government for moving forward with this first-of-its-kind underwater transmission line. It’s an exciting example of the province and city working together to build resilient, clean energy infrastructure that keeps costs down, supports good-paying jobs, and powers the projects that will shape Toronto’s future. We’re committed to creating an affordable and caring city that delivers for Torontonians.”

To keep costs affordable, the government is proposing the IESO launch a competitive procurement process to select a transmitter, which will be informed by a consultation on the procurement design. This approach will accelerate construction and create opportunities for Indigenous participation.

An underwater third transmission line will build system resilience by providing an option that is less vulnerable to extreme weather events such as flooding or ice storms, instances that have previously resulted in lost electricity supply and $100–200 million in costs and lost productivity.

The underwater cable will also deliver more capacity than any other option and meet the system needs beyond 2044, reducing the need for additional, costly upgrades and expansions. The third line will also alleviate strain on the bulk power system by avoiding bulk system reinforcements elsewhere in the GTA which could result in an estimated preliminary savings of $100–$300 million.

The development, construction and commissioning of the third line could take between seven to 10 years to complete.

The IESO’s recommendation follows extensive technical analysis of multiple options, prioritizing routes that minimize land-use impacts by leveraging existing corridors, underground infrastructure and pathways.

High-voltage underwater transmission lines are already in use in other Canadian jurisdictions such as Newfoundland and Labrador, Nova Scotia, and Prince Edward Island.