Why the Great Salt Lake’s causeway may have staved off collapse more than once

As the Great Salt Lake edged toward the brink of ecological collapse in recent years, Utah’s resource managers found sealing off its railroad causeway was one of the quickest and cheapest ways to save it.

Turns out, the causeway has likely kept the over-tapped lake viable for decades, allowing multimillion-dollar lake-based industries and massive flocks of migrating birds to thrive.

“When I first started working on the lake, people would say, ‘We should remove the causeway. It’s not natural,’” said Bonnie Baxter, director of the Great Salt Lake Institute and a biology professor at Westminster University.

But as the Great Salt Lake shriveled to record lows in 2021, and again in 2022, scientists and lake advocates realized the role the structure has long played.

“It became clear that the ecosystem that we needed to preserve is in the south arm,” Baxter said. “So the causeway has a purpose.”

Trains have traveled across the Great Salt Lake via the Lucin Cutoff for more than a century. The route started out as a wooden trestle that allowed water to move freely across the lake, keeping its salinity concentrations mostly consistent. That changed in 1959 when the railroad operators replaced the Lucin Cutoff between Promontory Point and the West Desert with a rock-filled dike. It effectively sealed off Gunnison Bay, sometimes called the lake’s north arm, from any sources of fresh water, since the lake’s tributary rivers empty into other bays.

Rail companies engineered the causeway to include two culvert openings and allow water to flow north, but filling in the route with rock transformed the Great Salt Lake in significant ways.

“[It] essentially divided the lake into the north arm and south arm,” Brian Steed, the Great Salt Lake Commissioner, told reporters this month. “That was not the intent at the time, but that’s been the de-facto result. ... We have seen, since the 1950s, this increased salinity in the north arm to the extent that we don’t have ecological vitality.”

Why the Great Salt Lake functions as two lakes, with two different colors

In order to maintain an ecosystem where flies, brine shrimp and millions of migrating birds thrive, the Great Salt Lake needs about 120 to 160 grams of salt per liter. That’s a salinity concentration of about 11-14%.

The causeway turned the north arm into a salt sink. Water only leaves the Great Salt Lake lake through evaporation, leaving its salts and minerals behind. With little freshwater inflows reaching the north, its water has dissipated away over the years, concentrating the brine down to about 25-30% salt.

It is so salty in the north that minerals precipitate out of the water and form a crust on the lakebed. When the lake was connected as one, salt crusts would re-dissolve and mix around with a fresh surge of spring runoff, but that doesn’t happen in the north arm anymore. Instead, it hoards salt away in its ever-growing lakebed crust.

The only life the north supports are salt-loving microorganisms that turn the water an otherworldly shade ranging from pink to purple to red.

The effect the causeway had on the Great Salt Lake is obvious in satellite images, where its hypersaline north appears distinctly different from its more productive southern reaches.

That transformation happened in a matter of years.

Thomas Caldwell Adams, an engineer who spent decades sailing the Great Salt Lake, advocating for the restoration of the Saltair lakeside resort and fighting against Kennecott Copper’s proposal to dump toxic mine tailings in the lake’s water, published a report in the journal Science just five years after the causeway finished construction.

“Interchange of saline lake water between the northwest body of Great Salt Lake ... and the main body of the lake,” Adams wrote, “has been severely restricted by the completion of a railroad embankment across the lake in 1959.”

Around one-quarter of the lake’s salt had migrated north, he reported, and the north arm had formed a crust about one foot thick.

“Further important effects,” Adams wrote, “on the entire lake are expected.”

By the end of the 1960s, Robert Smithson began exploring the north arm for a site to build his famed Spiral Jetty earthwork sculpture. The artist was lured by the lake’s “wine-red” color. The lake’s transformation was complete.

“That’s only 10 years,” Baxter said. “Think about it — that’s not a long time.”

In 1963, when Adams documented his findings, the lake was also plunging toward an unprecedented low elevation. The engineer was more concerned over the nascent minerals extraction industry, which would later balloon into a billion-dollar economic engine, than the lake’s ecology. He made no mention of brine shrimp, brine flies or birds.

Adams did, however, warn of the public health risk a shrinking lake posed.

“A lower surface level [will] result in a large expanse of dry lake bed,” he wrote, “which will become a place of origin for dust storms.”

Today, the north arm’s mineral crust is 8 feet thick or more in places, according to information from the Utah Department of Natural Resources. Its water level is again teetering at record lows, and even with a few years of high runoff in the 1980s, and an unprecedented snowmelt in 2023, it continues a long-term course of decline.

While dust storms remain a concern, sequestration of the lake’s salt over the decades may have prevented the lake from collapsing many times over.

As Mormon Pioneers and other settlers started building cities, farms and reservoirs that siphoned away the lake’s tributary streams, it began its 200-year receding trend. By the 20th Century, records and research show the lake’s salinity often spiked to concentrations that would have caused its ecology to crash.

“We can look back into history,” said Ben Stireman, a deputy director with the Utah Division of Forestry, Fire and State Lands, “and see lake salinity levels were quite high before that causeway was put in.”

Baxter has found old University of Utah theses from the 1930s that showed salinity levels at 23% across the lake. Adams himself, who sailed the Great Salt Lake during that period, noted in his paper that the lake “frequently” reached salt saturation before the causeway’s construction.

But those spikes were likely short enough for the ecosystem to recover.

“The lake never turned pink. People would have written about that, right?” Baxter said. “I don’t think it was hypersaline for long enough to grow those microbial communities until the north arm was segmented.”

But adding the causeway and turning the north into a salt sink created more consistency for the rest of the lake’s salinity. It coincided with the rise in brine shrimp harvesting businesses in the 1990s, which in turn supports a farmed seafood industry that feeds much of the world. It has allowed the lake to continue to host more than 300 species of birds every year, including ducks, grebes, gulls, ibis and avocets, even as other water sources in the West dry or get diverted away.

Why the Great Salt Lake is worth saving — even if it means sealing off its northern reaches

That the lake recovered despite historical spikes in salinity shows its resilience, Baxter added.

“Every life form in a salt lake has flexibility baked in,” Baxter said, “because they have to have a way to manage hard times.”

Brine shrimp have adapted to lay hardy cysts that can survive a wide range of extremes and then hatch into the next generation when conditions improve. It’s why the aquaculture industry collects them, packages them and ships them across the planet.

Brine flies seek out pools of fresh groundwater seeps, Baxter said, when the lake gets too salty — something she observed during the lake’s lowest documented elevation in 2022. They can then reproduce in droves when the lake’s salinity returns to the optimal zone.

“The flies were so robust this [past] year,” Baxter said, “it’s almost like they were saying, ‘Look what I can do, just give me some water.’”

The migrating birds that feed on the flies and shrimp historically adapted by flying to other saline lake systems in the West when one lake became too salty to support them. But disturbances caused by humans, including climate change and water consumption, have made it harder for those birds to adjust. The Great Salt Lake is one of the last viable stopovers left as they make their long journeys across the Western Hemisphere.

“Our concern is that is when the south arm gets too salty,” Baxter said, “the invertebrates can’t handle it. And then the birds stop coming, or they come and they die.”

The north arm — which is basically all of Gunnison Bay — offers a warning of what might happen to the rest of the Great Salt Lake if its salinity spikes for an extended period. There are no brine shrimp or bugs. It’s mostly devoid of life, other than a large nesting colony of American white pelicans who raise their chicks on Gunnison Island every year, tolerating its extreme environment to benefit from the seclusion.

To avoid a similar fate for the rest of the lake, the Division of Natural Resources’ Salinity Advisory Committee recommended raising a breach in the causeway by several feet to stop the exchange of water between north and south.

Stireman’s division moved ahead with the proposal in 2022, with the governor’s blessing. It made a dramatic difference in lake levels. Gunnison Bay currently sits about 3 feet lower than the rest of the lake. But the scientists who supported walling off the north arm weren’t concerned about making the rest of the lake higher — they wanted to block water in Gunnison Bay’s salt sink from flowing south and making things worse.

“None of this is really about ‘How high is the water?’” said Baxter, who is a member of the committee. “The biology is driven by the salinity.”

Raising the berm also had the side benefit of eliminating a deep brine layer that forms in the Great Salt Lake as the saltier and much heavier northern water moves south.

This denser water lingers at the bottom and creates an environment devoid of oxygen. Microorganisms in that briney layer then convert elemental mercury into methylmercury — a toxic form of the chemical that moves through the food web.

Scientists have documented elevated levels of mercury in spiders and waterfowl at the Great Salt Lake for decades, which feed on brine flies that pupate several feet below the water surface.

“When you build this berm, you prevent that heavy brine from coming in,” Baxter said.

Fresher water can still pour over top of the breach and reach Gunnison Bay when the lake is high enough, but the raised berm prevents the deep brine layer and methylmercury from forming.

Still, scientists and resource managers are clear — sealing off the north arm isn’t a permanent fix for the Great Salt Lake’s many problems.

“To me, the goal is to return the lake to its optimal surface elevation,” Stireman said. “I don’t think this berm or any engineered solutions are meant to replace getting water back to the lake.”

Although Gunnison Bay will likely never again support the abundant invertebrates and birds seen in other parts of the Great Salt Lake, it still serves a purpose. It helps the state manage salinity, supporting both wildlife and a robust aquaculture industry. It provides a place for water to flow during extended periods of high runoff. And its islands serve as refuges for nesting birds — like the solitude-seeking pelicans, who vanished from the north arm last summer after years of low water.

“Which I’m really worried about,” said Baxter, who has studied Gunnison Island and its visiting birds. “It’s a temporary solution. There’s no way this can work long term if the amount of water coming into the lake doesn’t change.”

This winter, salinity advisory committee recommended raising the breach even higher. State officials, however, declined.

“From a policy perspective, I don’t think we’re ready to give up on the north arm,” said Steed, the lake commissioner whose job includes overseeing management of the causeway berm. “And I don’t think we’re ready to say that the north arm is going to be something that we’re just going to sever.”

This article is published through The Great Salt Lake Collaborative: A Solutions Journalism Initiative, a partnership of news, education and media organizations that aims to inform readers about the Great Salt Lake.