Danger ahead: Saving St. Anthony Falls

You may have seen recent news reports about St. Anthony Falls being in danger of collapse. It’s an important issue for the City of Minneapolis and the municipalities that depend on Minneapolis to deliver clean drinking water taken from the Mississippi. To understand what’s going on, let’s take a trip back in time.

The glacial age

The falls have been eating themselves alive for millennia. Geologists estimate they started when the glaciers retreated from Minnesota 12,000 years ago. The falls were located in what is now downtown St. Paul and are thought to have been 2,700 feet across and 175 feet high. They’ve been moving westward ever since.

About 10,000 years ago, the sandstone beneath the limestone bedrock of the river had eroded to the confluence of the Mississippi and Minnesota rivers, where the waterfall split in two: Minnehaha Falls and St. Anthony Falls.

Dakota people in the area viewed the falls as a spiritual place. They called it Owámniyomni, meaning “turbulent water” or “whirlpool.” According to Owámniyomni Okhódayapi (formerly Friends of the Falls), which was recently given possession of the St. Anthony Falls Lock and Dam, they came to Owámniyomni for ceremonies and to Spirit Island, an island lost during construction of the lock, to give birth. “This was – and is – a place of gathering, trade, and offerings. It is a place where the physical and spiritual worlds blend, and where, through Dakota oral history, we learn about interactions with Uŋktéi (Water Being or Water Monster).”

The Ojibwe were also familiar with the falls and called it Kakabika, or “severed rock.” A painting by George Catlin made in 1835-36 shows a group of Ojibwe portaging around the falls.

The age of exploration

John Anfinson, historian and former superintendent of the Mississippi National River and Recreation Area, wrote in a 2003 article in Minnesota History, “Native Americans had the river to themselves” until 1680, when French explorers Antoine Auguelle (Picard du Gay) and Father Louis Hennepin traveled downriver from a Dakota village near Lake Mille Lacs, where they were either guests or captives (there’s a dispute over the right term). Accompanied by Dakota guides, they became the first white men to see the falls.

The Franciscan priest was so impressed by the falls that he named them after his order’s patron saint, St. Anthony of Padua. The name stuck. Hennepin estimated the height of the falls at 40 to 60 feet.

He was followed by Jonathan Carver in 1766, who made the first drawing of the falls. He lowered the estimated height to 29 feet. In 1805, Lt. Zebulon Pike came in with an estimate of 16.5 feet.

Since Hennepin and Auguelle saw them, the falls have moved 1,500 feet upstream.

The age of exploitation

After the explorers came the exploiters: men who saw economic opportunity in falls. Dams were built on both sides of the river. Between 1821 and 1823, Col. Josiah Snelling, commander of Fort Snelling, ordered a sawmill and grist mill built on the west bank. From Franklin Steele, who built the first commercial dam and sawmill in 1848, to William W. Eastman and John L. Merriam, who tried to build a tunnel under the falls for Minneapolis’ flour mills in 1869, men sought to harness the river.

By the 1850s, manufacturing took place on both sides of the falls. The mill district was a warren of 2.9 miles of tunnels and open canals. The falls had receded 35.5 feet per year by 1852, Jean Lamm Carroll wrote in a 2015 article for the U.S. Army Corps of Engineers (USACE). “Between 1857 and 1868, the waterfall was receding at an average of about 26 feet per year and coming perilously close to the limits of the limestone cap.”

Eastman and Merriam, who had just acquired Nicollet Island, made an agreement with the St. Anthony Company to share water rights so they could build a mill. The agreement allowed them to excavate a tunnel under Nicollet and Hennepin islands.

Carroll wrote, “In September 1868, Eastman, Merriam and two additional partners began excavating the tailrace. The plans called for a 6-foot by 6-foot tunnel cut through 2,500 feet of sandstone. Workers began digging at the downstream end of Hennepin Island and by October 4, 1869, they had tunneled through 2,000 feet of sandstone, bringing them as far as the toe of Nicollet Island.”

The workers noticed water leaking into the upper end of the tunnel. It quickly became a deluge. The next morning, the river broke through the limestone shelf. A whirlpool formed and sucked everything into the tunnel. “As the roof of the tunnel fell in,” Carroll wrote, “Hennepin Island began to sink and the falls were in danger of collapsing.”

Saving the falls

Alarmed citizens rushed to the scene, chucking rafts full of dirt, rocks and debris into the whirlpool, only to have others pop up elsewhere. They asked the Corps for help, and in July 1870, Congress approved $50,000 to preserve the falls.

The falls continued to erode. After failing to plug the tunnel with concrete, Anfinson wrote, “the Corps in 1874 recommended building two low dams where the east- and west-side dams joined so that water would always flow over the central falls. The Corps also wanted to rebuild the timber apron started in 1866 to preserve the edge of the falls and, most importantly construct a massive wall from one side of the river to the other under the limestone cap.”

In an Oct. 2, 1904 Minneapolis Tribune article, Frank H. Wadsworth recalled how the wall was built. A shaft was sunk 75 feet through the limestone ledge on Hennepin Island. Stone was quarried from the foot of Nicollet Island to make concrete. “Gangs of men” continually worked on the wall, “relieving each other at intervals of eight hours.”

Geohydrologist Greg Brick, who has explored a small portion of the wall, told the Northeaster in an email, “The engineer’s letters laid out how the concrete was emplaced. Seems it was mixed on the surface, placed in narrow-gauge rail cars, dropped down through spouts to the lower level, shoveled into place manually and left to harden for 48 hours before the formwork was removed. Thus, the concrete was seamless, and not in the form of blocks, which would have left gaps for water to leak through. In Water Power Park, you can see the concrete itself where it pokes through to the surface, along the line of the cutoff wall.”

The completed wall is 1,570 feet long and 38 feet high. It is 6 feet wide at the base and 4 feet wide at the top. “The west end of the dike started 325 feet above the falls and runs across to Hennepin Island, then diagonally down it and then across the east channel above 200 feet above the east side dam,” Wadsworth wrote. A 3-foot-wide, 7-foot-high arched passageway used by the workers within the wall was filled in at the end of the project.

The federal government spent $615,000 between 1870 and 1880 to save the falls — almost $19.5 million in today’s money.

What lies beneath?

Construction of the wall and the wooden apron placed over the falls to protect them forever changed the look and sound of St. Anthony Falls. Instead of a jagged “coastline” of tumbled limestone blocks that stretches 1,500 feet across the river, the falls are confined to a width of about 350 feet. In 1955, Northern States Power Company (NSP), which is now known as Xcel Energy, replaced the wooden apron with concrete. Instead of tumbling over rocks, the river slides down the sheet. The tumbling water that could be heard from miles away can now be barely heard over the sounds of rush hour traffic.

It’s been 149 years since the wall’s completion. In 1885, the Corps turned maintenance of the waterfall back to the water power companies and the City of Minneapolis. In a February 2025 Star Tribune podcast, Anfinson noted that Xcel has made “short sprints of (Falls) monitoring,” but there has not been a comprehensive look at the wall. Anfinson said 90% of the wall cannot be inspected.

A couple of people have tried.

One was Minneapolis Tribune reporter Fletcher Wilson, who took a tour of what remained of the Eastman tunnel with members of the University of Minnesota’s St. Anthony Falls Lab in 1940. Tired of plowing through muck and mud, the party stopped short of the wall.

Hydrogeologist Brick went farther. In 1992, he got permission from the lab to explore the tunnel. He came across crawdads and clams and waded through waist-deep mud. In his book, “Subterranean Twin Cities,” he wrote, “I arrived at the concrete bulkhead, a total distance of one hundred feet from the walkway. I noted a little bit of leakage, but it was ‘nothing to worry about,’ I was later informed by officialdom. NSP had pumped tons of concrete into the tunnel years earlier to forestall any further problems.”

Anfinson, who chairs the board of Friends of the Mississippi River, testified to the Minnesota Legislature in 2023. “The cutoff wall qualifies as a Class 1 dam by state definition and as a high-hazard dam by federal guidance. Such dams should be inspected every one to two years,” he said. “If the cutoff wall failed and we couldn’t get control, the river would begin cutting down its bed. Anything resting on the limestone could collapse, including the 3rd Avenue Bridge and the horseshoe dam. If the reservoir above the horseshoe dam drained, Minneapolis, the suburbs it supplies and the International Airport could lose their water in days.”

Without the falls, a series of rapids could stretch from Northeast to Coon Rapids.

Brick said, “The common assumption that an underground cut-off wall is the equivalent of a surface dam is fallacious. It’s an easy analogy to make, but it’s wrong, in my opinion. The groundwater on the upstream end would deepen and build up pressure if there was nowhere for it to go, so the purpose of the cutoff wall is not to completely sever groundwater flow, which would create its own problems, but to slow the groundwater down to non-erosive (or what an engineer would call laminar) velocities, traveling through pores in the sandstone, rather than self-enlarging erosive voids that would undermine the structure. It’s a delicate balancing act.”

State Rep. Sydney Jordan, who represents NE, was the chief author of a 2023 bill that allocated $750,000 to the St. Anthony Falls Lab to assess the wall, using ground-penetrating radar. High water has kept them from completing their work; the Legislature expects a report in 2026.