The biggest lesson, simply put, is that bitumen sinks.
"Everybody learned from this incident about what we can do differently. Every one of us, from the regulators, to the contractors, to ourselves, have come away from this saying, 'I know what I would do differently the next time,'" explained Leon Zupan, Enbridge's chief operating officer.
The U.S. Environmental Protection Agency has ordered Canada's largest pipeline company to return to the river to dredge areas where the agency believes remains of the heavy bitumen fossil fuel have collected. The March 2013 order came nine months after most of the 56-kilometre stretch of the river affected by the spill was reopened to the public.
The Kalamazoo incident is the largest inland spill in the history of the U.S., and has already cost Enbridge more than $1 billion.
The EPA believes there is at least 684,000 litres of bitumen still in the river. Before March's cleanup order was issued, Enbridge and the EPA went back and forth over how much oil there was and whether or not dredging it would do more harm than good to the Kalamazoo's ecosystem.
In the end, the EPA prevailed.
"They [Enbridge] don't agree with the way we develop our number. And, you know what, we're the agency and I'm not going to let them dictate how we do science," said Jeff Kimble, the EPA's incident commander in Marshall, Mich.
Bitumen sinks in fresh water
Scientific differences aside, the company agreed to the regulator's demand and began its work in August.
For Enbridge and the EPA, the main lesson from the last three years is the need to recover the diluted bitumen, or dilbit, as soon as possible.
"If you know up front that you're dealing with an oil that has the potential to sink, attack it right away and get it off the surface while you can," explained Kimble.
Enbridge agrees. "If you can err in doing some damage to get the oil out sooner, then the long-term impacts are greatly mitigated," said Zupan.
For Enbridge, though, the Kalamazoo experience changed more than just the way it responds to emergencies. Zupan said the company's whole culture around safety is now different.
"We've redefined what's important to the company. We've added to our practices and procedures. We thought we were pretty good. We want to be the best," Zupan told CBC News.
But some in the area of the spill aren't buying that. Deb Miller of Ceresco, Mich., just down the road from Marshall, doesn't trust anything she hears from Enbridge or the EPA.
"I was absolutely naive going into this. I probably trusted more than I should have. I took things at face value that I should have never," explained Miller.
Miller's house backs on to the Kalamazoo River. When the spill happened, she was undergoing chemotherapy and her doctor ordered her to stay inside to escape the asphalt-scented fumes that permeated her village. From the beginning, she said, company and government officials have given conflicting and changing orders and advice.
"EPA has been very, very vocal in admitting the fact that they're writing the book as they go along on this spill," she said. But, she said, Enbridge is the real villain.
"Enbridge does what they have to do and only that," said Miller. She understands that the company is a for-profit business and that guides many of its decisions. But her life and town changed radically after the spill.
She and her husband had to shut down their carpet store. Enbridge bought the building but not the business.
Many of her neighbours moved away.
"When it affects people, residents — there's a high road and there's a low road. And unfortunately, I think they [Enbridge] found that low road."
Enbridge lived up to its promise
For Dr. Jim Dobbins, a retired family doctor and vice-president of a local conservation society in Marshall, that assessment of the company might be a little harsh. He admits he was sickened and angry as he watched the oil course under the bridge that spans the Kalamazoo just west of town. But when then Enbridge CEO Pat Daniel addressed a community meeting in Marshall soon after the spill, he decided to give the company a chance.
"[Daniel] said, 'We've made a mess and we're going to clean it up,'" recounted Dobbins. He admits to being pleasantly surprised.
"I'm not angry at the company," said Dobbins, although he is rankled by the spill.
"But generally, it appears as though they have done what they said they would do. And that is clean up the river."
He also thinks the EPA has gone too far with this latest order to re-dredge the river.
"I'm very concerned about them doing more damage to the river than [they] are good by retrieving that amount of oil that's left," said Dobbins. He thinks it is all about the EPA throwing its weight around rather than worry over the Kalamazoo's ecosystem.
Kimble explained it differently.
"You know, bottom line for EPA is under our authority this is oil that's causing a sheen or a release on a navigable waterway. Our authority says and our law says, get it out of the system."
That is precisely what Enbridge is doing. And, like everyone else involved in this incident, hoping to learn something in the process.
"The legacy for us is not that you can clean up a major oil spill after it occurs even though the river looks great today. The legacy for us is how do you make sure it never happens again," said Zupan.