Ontario approves $1.5B underwater transmission line to Toronto
Officials say without the line, Toronto would have to turn down investments and reduce housing.
Key Takeaways:
- Ontario has approved an underwater HVDC transmission line from near Darlington into Toronto to add up to 900 MW, with the province warning current supply paths start hitting capacity limits in the 2030s as demand climbs toward 2050.
- It will require new/expanded terminal facilities, extensive permitting and marine/shoreline work, and could take 7 to 10 years, with the IESO targeting an in-service date around 2034.
- The IESO will run a competitive transmitter selection process, the IRRP pegs the recommended option around $1.5B, and specialized HVDC equipment has multi-year manufacturing lead times that can affect schedules.
The Whole Story:
Ontario has approved a plan to build a new high-voltage underwater electricity transmission line into Toronto, a project the province says is needed to keep pace with growth as demand in the city is expected to rise sharply in the coming decades.
Energy and Mines Minister Stephen Lecce said the province is moving ahead after accepting a recommendation from the Independent Electricity System Operator to build a third supply path into Toronto from near the Darlington Nuclear Generating Station, aiming to deliver up to 900 megawatts of additional power.
“Without a new transmission line, Toronto would have to turn down job-creating investments and reduce housing,” Lecce said.
The province says Toronto is currently supplied by two main transmission pathways — from Manby Transmission Station in the west and Leaside Transmission Station in the east — and that both are expected to begin reaching their limits in the 2030s.
The IESO’s 2025 Toronto Integrated Regional Resource Plan recommends an underwater high-voltage direct current line delivering supply toward the Hearn Switching Station, with an expected in-service date of 2034. The report describes the project as a major infrastructure build requiring route studies, permitting and approvals, and significant station work at both ends of the connection.
Mayor Olivia Chow welcomed the decision, calling it “an exciting example” of the city and province working together to build clean energy infrastructure that supports housing, transit and jobs.
To rein in costs, Ontario says it wants the IESO to run a competitive procurement to select the transmitter — a process that would be informed by consultation on the procurement design. The province also says it wants the approach to create opportunities for Indigenous participation.
Beyond capacity, the province argues the underwater route would improve resilience by being less exposed to extreme weather, while also reducing pressure on the bulk power system. The IESO plan estimates the recommended underwater option at roughly $1.5 billion in capital cost and notes it could avoid up to $300 million in broader bulk-system reinforcements compared with other options.
From a construction perspective, the IRRP highlights the need for specialized HVDC equipment and points to long lead times in the supply chain: once a project is in a manufacturer’s production queue, timelines can run several years. That dynamic, the report suggests, makes early action critical if Ontario wants to hit the targeted in-service date.
Ontario says development, construction and commissioning could take seven to 10 years — and argues that acting now is essential to keep major housing, transit expansion and job growth on track in the province’s largest city.