Toronto Third Line
The Toronto Region is entering a period of unprecedented growth, with electricity demand in the city expected to double over the coming decades. To ensure the region has the reliable and affordable power needed to support new housing, transit expansion, and economic growth, the IESO is proceeding to build the Toronto Third Line—an innovative transmission project connecting downtown Toronto to Bowmanville via Lake Ontario.
The IESO has launched a competitive procurement process for the Toronto Third Line project—the underwater transmission line will be the first of its kind in Ontario—that will ensure a transparent and cost effective approach to selecting a transmitter to design, build, and operate the high-voltage line. Designed to strengthen grid resilience, diversify supply pathways, and relieve emerging constraints on the existing transmission system in and around Toronto, the project represents a critical investment in the city’s energy future.
Once in service, the Toronto Third Line will help power hundreds of thousands of homes and businesses while supporting long term planning for a resilient, affordable electricity system across the Greater Toronto Area and beyond.
Any general enquiries regarding the Toronto Third Line or the Transmitter Selection Framework (TSF) can be sent to TSF@ieso.ca.
TSF Registry
The TSF Registry is active and currently open for the Toronto Third Line Project.
The TSF Registry represents the first step in implementing a competitive transmission procurement and will enable transmitters to participate in future IESO competitive transmission procurements.
The registry will help identify transmitters to ensure a pool of experienced and capable proponents is in place—allowing procurement processes to move forward efficiently as transmission projects are identified.
All TSF Registry submissions made after January 28, 2026, must include a completed Non-Exclusivity Attestation Form.
Please see the Successful Registrants List (March 27, 2026)