Most of the people drawn to the recreational pleasures of the St. Croix River might not know that 2.5 million barrels of oil course daily through pipelines beneath its headwaters — and that more could be on the way.

By year's end, energy giant Enbridge will finish 15 new pump stations to push heavy crude oil faster through Line 61, a 42-inch buried pipeline in northwest Wisconsin that runs beneath the environmentally sensitive St. Croix and three other rivers that feed it.

Enbridge also has done preliminary work on a twin pipeline that would run parallel to Line 61 and add as much as 800,000 barrels of oil to the current flow beneath the St. Croix, Eau Claire, Totogatic and Namekagon rivers.

"If those pipes were to rupture into the St. Croix water, you could have environmental damage all along a wild and scenic river," said Richard Smith, president of Friends of the Headwaters, a citizen group that opposes Enbridge's proposed pipelines through lake and river country in Minnesota and Wisconsin.

Jennifer Smith, Enbridge's stakeholder relations manager, said the company recently invested in a new pipeline control center, better leak detection technology and hundreds more annual inspections to meet its goal of zero accidents.

"Safeguarding water is nonnegotiable. There is no room for debate there," she said Friday.

The company's directors haven't yet approved construction of the twin line, known as Line 66. But an Enbridge executive said last fall that a new pipeline might be needed to carry extra oil the company wants to ship from Canada to its terminals in Superior, Wis.

Line 61 pumps 900,000 barrels daily from Superior to a terminal in Illinois and is the largest of four Enbridge pipelines currently operating in the corridor, Jennifer Smith said. When Enbridge completes its expansion in December, Line 61 will have a daily capacity of 1.2 million barrels.

Three southbound lines carry batches of different oils, including tar sands oil from Canada and lighter crude from the Bakken oil patch in North Dakota. The fourth line flows north from Illinois, transporting a hydrocarbon known as diluent or condensate that's used to dilute heavier oils for the journey south.

"The likeliness of an oil spill, they're relatively rare," said Jennifer Smith, who works at Enbridge's office in Duluth.

'Rolling the dice'

Nevertheless, environmentalists say the dangers of piping so much oil through the St. Croix watershed can't be overstated.

The St. Croix River, considered pristine by today's standards, is federally protected and comes under strict inspection for pollution of any kind. The National Park Service oversees the St. Croix and Namekagon rivers, which together make up the St. Croix National Scenic Riverway.

About a half mile of Line 61, which began operation in 2009, cuts through the riverway's park boundaries, said Jill Medland, who oversees natural resources at the park service headquarters in St. Croix Falls, Wis.

Enbridge owned right of way land through the St. Croix headwaters before the riverway was established in the early 1970s, she said. But now Congress would have to approve any proposals for a twin pipeline that would cross riverway boundaries.

Jennifer Smith said that if Enbridge decided to build Line 66, people could expect town meetings, open houses and conversations with landowners. The project would require permits, she said, and "the public would be made aware that we were planning to move forward."

Environmentalists point to an Enbridge spill in 2010 as reason for concern for the St. Croix headwaters. An older pipeline ruptured and poured 20,000 barrels of oil into the Kalamazoo River in Michigan, leading to one of the costliest inland cleanups in U.S. history.

Jennifer Smith acknowledged the spill as "one of the darkest days in Enbridge's history," but said it led to $4 billion in investments in pipeline technology and other changes, such as doubling the number of people who monitor leaks.

"Enbridge is a safer company today for that," she said.

The ruptured pipeline was carrying the controversial tar sands oil, a substance thick, like peanut butter, that must be diluted with chemicals to move it through the pipe. When a rupture occurs, the chemicals dissipate but the sticky oil sinks to the bottom, clinging to rocks and riverbed.

Environmentalists say any oil leak into the four rivers that eventually merge into the St. Croix would be quickly swept downstream by the fast current and into the pristine areas people love most.

"A lot of people don't understand what the potential risk is," said Deb Ryun, executive director of the St. Croix River Association. "If there was a massive spill it would be absolutely devastating and probably unrecoverable."

Given the increased pressure flow in Line 61, she said, a half-hour spill would pour as much oil into the St. Croix River as the 18-hour spill in the Kalamazoo.

"We're really rolling the dice on one of the treasures of Wisconsin, at the expense of the citizens of Wisconsin and our natural resources, for corporate gain," said Carl Whiting of the Wisconsin Safe Energy Alliance. "We're in a position now to say, 'Let's raise these questions before there's a major disaster.' "

Monitoring for leaks

Medland said a new riverway spill-response plan will determine where a spill would threaten the river's water quality, aquatic health and fish populations in the St. Croix's most pristine areas.

Richard Smith, a professional photographer who lives in Hubbard County, Minn., said the Friends of the Headwaters group doesn't necessarily oppose oil pipelines. It just prefers a route through southern Minnesota.

Running pipelines near lakes and streams, as Enbridge proposes with its Sandpiper project in northern Minnesota, endangers drinking water, recreation and tourism, he said.

"There is no public good in this project," he said. "You have a foreign company for private gain, and we assume the risk."

Jennifer Smith said Enbridge uses thicker-walled pipes through waterways, and that flows are shut down automatically within three minutes of a detected leak. Pipes are coated to resist corrosion and monitored by computers around the clock, she said. And the company has compiled detailed emergency response plans.

But Ryun said no amount of preparation can guarantee protection against unthinkable damage.

"Acts of God happen, accidents and human error happen, and machines malfunction," he said. "It's as simple as that, isn't it?"