Hennepin County Commissioner Mike Opat wants to build a curved promenade of nearly a mile that would span the Mississippi River and put pedestrians just above the dam leading to the St. Anthony Falls spillway.

The proposed "Wishbone" would be the splashiest new development concept for the Mississippi riverfront in downtown Minneapolis in recent history.

"Great cities have great public spaces," said Opat, who envisions the project as something like New York City's High Line, the popular 1.45-mile elevated linear park along a former rail line on the west side of Manhattan.

Opat will make present the idea to the public Tuesday, along with the "very preliminary" cost estimate of $50 million to $100 million. He said that Hennepin County would be a partner, and not necessarily the lead, on the project.

It's a complicated project, but Opat has shepherded large, controversial projects before. He put together the financing that got the Minnesota Twins into a new ballpark, Target Field, in 2010.

Though this project would be less expensive, it would be trickier because of the extensive number of public and private groups with an interest in the river. As Opat put it: "Nobody owns it and everybody owns it."

Besides the city and the county, there would be federal agencies, environmentalists and Xcel Energy, which runs a nearby power plant. And that's just for starters.

The Minneapolis Park and Recreation Board likely would play a major role in reaching out to the public and leading discussions about it. Michael Schroeder, assistant superintendent of planning for the board, said Wishbone is "not inconsistent with our plans for the riverfront or the river in general."

He noted that others have presented ideas for that stretch of the river as well, including Friends of the Lock and Dam. Last fall, that group announced it had raised $5 million for a plan to remake the area — which includes the decommissioned lock — into a visitor center with boat access, riverfront dining, underground parking and event space.

Opat said Wishbone complements that plan. Schroeder didn't disagree, saying both ideas are "oriented to getting people more engaged with the river, especially around the falls." He said lots of proposals are being floated.

"I don't know that the Park Board would turn its back on any of them at this point," he said.

John Anfinson, superintendent of the Mississippi National River and Recreation Area — the National Park Service unit that oversees the river's 70-mile corridor through the metro area — said he liked the idea.

"Anything that can help people understand the significance and power of St. Anthony Falls is a good thing," he said. The Wishbone design has the potential to do that by putting pedestrians on top of the falls, which launched worldwide food brands like Pillsbury, Betty Crocker and General Mills.

But Anfinson said he would like to see the details. The project would have to be done in a way that protects the river and the surrounding area as well as educates the public, he said: "We have one of the most special sites on the whole river."

Publicly financed downtown riverfront attractions have proved expensive for taxpayers to maintain and repair.

The Stone Arch Bridge in downtown Minneapolis was at risk for closure last year before it secured $15 million in state and federal funding for needed repairs. The state turned to federal funds after state leaders failed to set aside enough money for the repair work, Minnesota transportation officials said at the time.

Commissioner Jan Callison, who said she was briefed on the proposal earlier, has lots of questions, including who would pay for construction and maintenance.

"I appreciate the thought that's gone into it and the vision and the concern for the region," she said. "It's a serious proposal, clearly."

Dave Norback, president of RSP Architects in Minneapolis, created the Wishbone concept after brainstorming about how to better connect the city to the river. He will describe the design in more detail at Tuesday's County Board meeting.

In his view, timing for the project works because industry has moved off the river, the federal government has closed the lock and dam and the riverfront is growing.

The walkway would bring "the public close, creating an intimate connection to the river — a place to walk, run, bike, or rest alongside the majestic power and beauty of the Mississippi," he said.

Norback, who has done extensive research, said that about 80% of the infrastructure needed for the promenade already exists. For example, the mooring cells that used to guide boats into the lock and dam could be used as structural supports for the walkway, while the lock itself would become a grand staircase and elevator.

"Accessible from both sides of the river, the hope for the landscaped walkway is that it would be free to the public, open year-round and feature a range of programming possibilities," Norback said.

Opat and Norback have been speaking privately for years to numerous parties who might have a say in whether the project goes forward, including policymakers, environmentalists and American Indian tribal leaders. The two said they've taken the concept around, looking for red flags. They also acknowledge it's early in the process and that concerns have yet to be aired.

After Tuesday's presentation, the County Board could seek a feasibility determination to get a sense of whether commissioners — and the public — consider the project worth pursuing.

Schroeder said the Park Board could help coordinate public discussion about the proposal and acknowledged it would be a long, complicated process to get needed approvals. He added: "Just because something's difficult, doesn't mean we shouldn't do it."

Rochelle Olson • 612-673-1747 Twitter: @rochelleolson