Pipeline company operators based in Edmonton waited over an hour to shut down the line after noticing a drop in pressure.

The Line 3 pipeline was also the origin of a 1.3 million gallon oil spill in Argyle in 1973, the second worst in Minnesota history.

[3] Officials with the Minnesota Pollution Control Agency estimated that a total of 5.7 million gallons had spilled from the Lakehead line since 1971.

[4] On the morning of March 3, 1991, an underground section of the Line 3 pipeline ruptured on a 16-acre wetland owned by Harry Hutchins.

[4] Following the rupture, a geyser of pressurized oil sprayed 30 to 40 feet in the air, coating aspen trees in the area.

[2] Two more hours passed before the company shut off valves to isolate the ruptured section of pipeline and prevent more oil from spilling.

[2] According to the National Oceanic and Atmospheric Administration, the delay in shutting down the pipeline resulted in a significant increase in the volume of oil that was spilled.

[5] Fish were killed where oil entered the water and the spill impacted marshes and vegetation on the riverbank.

Had the oil spill occurred a month later when the ice had melted, hundreds of miles of the Mississippi River could have been affected.

[13][14] As of December 2020, Enbridge is constructing a new, larger pipeline to carry oil from Canada and replace a portion of Line 3.