Toronto Third Line

The Independent Electricity System Operator (IESO) is conducting a competitive procurement process to select a transmitter for the Toronto Third Line project, an innovative underwater transmission line connecting downtown Toronto to Bowmanville via Lake Ontario. This project represents a critical infrastructure investment to support unprecedented growth in the Toronto Region, where electricity demand is expected to double over the coming decades.

The Toronto Third Line will be the first underwater transmission line of its kind in Ontario and is designed to strengthen grid resilience, diversify supply pathways, and relieve emerging constraints on the existing transmission system in and around Toronto. The selected transmitter will be responsible for designing, building, and operating the high-voltage transmission line. The project supports new housing development, transit expansion, and economic growth by ensuring the region has reliable and affordable power for hundreds of thousands of homes and businesses.

The IESO has established a Transmitter Selection Framework (TSF) Registry as the first step in this competitive transmission procurement process. The TSF Registry enables transmitters to participate in the competitive procurement for the Toronto Third Line and future IESO competitive transmission procurements. Registry submissions received after January 28, 2026, must include a completed Non-Exclusivity Attestation Form. A Successful Registrants List was published on March 27, 2026, identifying qualified proponents.

The project timeline and detailed procurement requirements are available through stakeholder engagement sessions and the Toronto Third Line Digital Guide. General inquiries regarding the Toronto Third Line or the Transmitter Selection Framework should be directed to the contact information provided.