Earlier this month, the Senate failed to override President Obama’s veto of authorizing further work on the Keystone XL pipeline, a bill that would have allowed the final piece of the massive oil pipeline stretching from Alberta, Canada to the Gulf of Mexico to be built.

The president’s veto was hailed as a major victory by environmentalists and opponents of further oil developments, and conversely scorned by proponents who claimed it would create jobs and lower gas prices for Americans.

The bill is dead (for now), but it’s widely thought that Republicans will attach it to the larger transportation bill slated for later this year, according to The Hill. “This is coming back in the form of an infrastructure bill, a road bill that we are all voting for,” West Virginia Democratic Sen. Joe Manchin told the site.

But until then, environmentalists and the anti-oil crowd might do well to shift their gaze to a much larger pipeline looming on the horizon, one that’s largely flown under the radar, receiving minimal national media attention.  

Line 61, as it’s known, currently transports about 560,000 barrels of tar sands oil every day between Superior, Wisconsin, where it links up with its operator’s Canadian oil lines, and Pontiac, Illinois. But this year, Enbridge, the Canadian energy company that operates it, has plans to expand Line 61’s capacity to transport roughly 30 percent more oil than Keystone would if approved—about 1.2 million barrels per day. To do this, Enbridge needs to either add or modify 12 pumping stations to maximize flow. And according to Vice News, eleven of those have been approved and the company is moving forward.

North American crude oil production has seen drastic increases in recent years, thanks to the popularity and ease of methods like hydraulic fracturing, or fracking. But methods of transporting greater quantities of it are falling short, leading producers to turn to rail: since 2008, oil-by-rail figures have shot up more than 4,000 percent.

Pipelines like the Keystone and Line 61, some argue, provide a somewhat safer alternative to transporting crude oil by train—while oil trains have been found to spill more often, pipeline spills are much larger.

But spills aren’t the only concern. The model of train cars used for oil transport, the DOT 111, are also known as “bomb trains,” given their tendency to explode when they derail, creating a serious danger for the communities they pass through. The most infamous example was in 2013, when an oil train derailed and exploded in a small Quebec town, killing 47 people almost instantly, and spilling millions of gallons of oil. Four explosions have occurred over the past month in the U.S. and Canada, and in February, the U.S. Department of Transportation submitted a proposal to the White House pushing for stricter safety standards of oil train cars.

Even though pipelines don’t necessarily carry the risk of exploding, the environmental impact of their spills is often substantial. Opponents of Line 61 have pointed to a July 2010 spill, which saw more than 840,000 gallons of tar sands crude dumped into the Kalamazoo River from a pipeline operated by Enbridge. Oil was reportedly carried 35 miles downstream in the river, according to the Environmental Protection Agency, making it one of the largest ever inland oil spills in the U.S. Moreover, chemicals mixed with the tar sands crude oil to facilitate passage through the pipeline mixed with the air, generating toxic gases and forcing many people in the area to evacuate their homes, according to the New York Times.

Aside from noxious gases, the heavy tar sands in the crude sank into the river, which led to harmful dredging efforts to extract it. After a $1.2 billion dollar cleanup (exceeding the company’s $600 million insurance policy), Endridge wrapped up its efforts last summer, though the EPA claims that oil from the spill is still present in the Kalamazoo.

Because Line 61 itself does not cross international borders—therefore not requiring the same sort of approval as the Keystone does—it hasn’t garnered the sort of fierce national attention as Keystone, which it would dwarf. Its only administrative approval requirements come from the counties it passes through, who can grant Enbridge conditional use permits. The company’s only block at this point comes from Dane County, which postponed Line 61’s expansion in January citing concerns over the presence of safeguards in the event of another Kalamazoo-level spill.

“Just to put that in some context, the volume that we’re talking about here, in an hour’s time, if there is a spill, there would be more than 2 million gallons at that rate. That’s a lot of oil. Over 2 million gallons in one hour compared to 800,000 over 17 hours in Michigan,” Dane County Board Supervisor Patrick Miles, who chairs the County’s Zoning and Land Regulation Committee, told the local news site Madison Commons.

Other environmentalists have voiced concerns over the pipeline’s proximity to Lake Superior. “The Great Lakes are all connected, so if something really big happens, it could affect all of them,” Wisconsin Sierra Club’s Elizabeth Ward told Vice News. “They provide drinking water for 41 million people.”

For its part, Enbridge has invested billions in revamping the company’s safety protocols and response infrastructure, but that didn’t prevent a recent spill along one of the company’s major Canadian crude oil arteries that connects with Line 61. 

In an effort to cover their losses in the event of a major spill, Dane County representatives stalled an approval while they attempted to push Enbridge into taking out a larger insurance policy. But if that price is too high, Enbridge could either rethink that portion of the expansion, or sue the county, which they effectively threatened to do in November, when lawyers gave county officials an implicating white paper explaining that the county has no legal business attaching insurance riders to a use permit.

The company is currently waiting on a presidential permit to allow for more oil to flow in from Canada, the delay of which could potentially corrode relations between Canada and the U.S., with Canadian lobbyists pushing for acceptance of the Keystone plan. Washington has said that the Line 61 permit delay is procedural, not political.