GREEN THOUGHTS: The Environmental Dangers of Not Building Keystone XL. “Opponents of the proposed Keystone XL pipeline worry that if the crude coming down from Canada’s oil sands were to spill, it could be an ecological disaster for areas of the Midwest through which the line would run, which are also home to precious groundwater sources. But if Keystone is killed, the oil still will flow—and more of it might be transported by ship through dangerous waters.”