The junior U.S. senator from Washington state has gone public with her deep concerns about the Kinder Morgan pipeline.
Over Twitter and in an open letter, the Democratic Party politician has asked President Barack Obama to "engage" on this issue with Prime Minister Justin Trudeau.
The Trudeau cabinet recently approved the Texas-based energy giant's application to increase shipments of Alberta bitumen to Metro Vancouver from 300,000 to 890,000 barrels of oil per day.
Once the pipeline is completed, it will result in a nearly seven-fold increase in the number of oil tankers passing through Burrard Inlet.
Approximately 400 oil-filled vessels per year will make this journey, later moving through Haro Strait near Washington state's ecologically sensitive San Juan Islands.
From there, the ships will travel in Juan de Fuca Strait, which is next to Washington state's Puget Sound.
“A tar sands oil spill would create far reaching environmental and economic consequences in the Pacific Northwest,” Cantwell wrote in her letter to Obama. “Given the importance of the Pacific Coast to the United States, I urge you to engage with Prime Minister Trudeau and take action to protect the Puget Sound. It is critical that sufficient policies, response resources and regulations are in place before moving forward with construction of the Kinder Morgan Trans Mountain Pipeline Expansion Project.”