The Keystone pipeline leaked in Kansas. What makes this spill so bad?

https://www.npr.org/2022/12/17/ [login to see] /cleanup-for-keystone-pipeline-oil-spill-kansas
It's been over a week since TC Energy announced its Keystone pipeline leaked into Mill Creek in Washington County, Kan. Nearly 600,000 gallons of oil spilled into the waterway as well as the land surrounding it.

Environmental advocates say this is just the beginning to a cleanup that will likely take years.

Operators were alerted to an issue with the pipeline on Dec. 7. As of Friday morning, TC Energy says, 4,125 barrels of oil from the creek have been recovered of the estimated 14,000 barrels (about 588,000 gallons) reportedly lost in the spill.

Aerial footage of the leak from Nebraska Public Media shows the leak has affected a nearby pasture and residents' farmland.

Many initial details, like the cause for the spill, are still not clear. What is known is the type of oil that was being transported through the pipeline: tar sands oil, also called diluted bitumen.