The morning of June 5, 1976, bulldozer operators at the newly minted Teton Dam site on the border of Madison and Fremont counties in eastern Idaho worked feverishly to shore up seeping leaks in the giant rock and earthen berm that were discovered two days earlier. Behind the ill-fated dam, some 230,000 acre-feet of stored irrigation water destined for more than 100,000 acres of farmland pushed against the 10 million cubic yards of silt, soil, sand, gravel and rockfill used to build the structure, gathering energy with every drop the Teton River pushed into the new reservoir. At 10:43 a.m., the Teton Dam failed and sent a wall of water rushing across the fertile landscape known for growing everything from wheat and barley to Idaho’s famous potatoes.

Trees, homes, cars, and the drowned corpses of cattle and horses — as well as millions of cubic yards of topsoil — gushed through the communities of Sugar City and Rexburg. Farther downstream, below the confluence of the Henry’s Fork and the South Fork of the Snake River, much of Idaho Falls flooded. Some 70 miles downstream, the town of Blackfoot took its share of the failed reservoir’s floodwaters. Only the calm waters of American Falls Reservoir nearly 100 miles away from the failed dam site could slow the raging waters from the angry Teton River. When all was said and done, 11 souls were lost, the communities of Wilford and Roberts were under water, 13,000 head of livestock were killed, 4,000 homes were washed away, and some 3,500 farm buildings were simply gone. Property damage was in the hundreds of millions in 1976 dollars. By any barometer, the failure of the Teton Dam was an ecological and economic catastrophe.

“The water picked up a huge oil tank like a cork and away it went,” eyewitness Dale Howard told Time Magazine shortly after the disaster. “There was a beautiful grove of cottonwood trees down below, and they were snapped off like matchsticks. Later I could see the water out on the plain. It was almost like a surrealist picture; as the water hit some of the farm fields, you could see an eerie cloud of dust and mist rise up three to five miles away.”

Toni Anderson, was 11 years old and living in rural Rigby, Idaho, when the dam broke. As rural Idahoans are known to do, everyone pitched in to help those in need.

“We had a houseful of people who evacuated from the path of the river,” Anderson said. “I remember that all of the television stations were airing live footage of the disaster, and one of the ladies who had come to our house was watching the news. She pointed at the TV and said, ‘Oh my gosh, there goes my house.’ She literally watched her house get taken by the flood on television.”

In Idaho’s history, there have been 23 presidentially declared disasters. The failure of the Teton Dam is, to this day, the only one caused by the follies of man.

While the dam’s failure remains fresh in the minds of those who lived through it half a century ago, today’s climatic challenges are contributing to a continuing narrative that the dam, in some way, shape, or form, should be rebuilt. Evidence in support of this idea? The winter of 2025-2026 is among the worst in recorded history for Idaho, and the Teton Basin fared poorly. As of this writing, the basin’s snow-to-water equivalent for this time of year sits at 28 percent of median. While most of the reservoirs in the Upper Snake River drainage are full or nearly full, the coming irrigation demand will draw lakes down significantly, and there’s very little runoff that hasn’t already come off the surrounding mountains. It’s going to be a touch-and-go season for water in Idaho’s rivers, and irrigators are already preparing for the worst. It’s no surprise, then, that 50 years later, there’s still talk of adding another reservoir in eastern Idaho to store water, particularly as a series of droughts since 2000 have plagued the region. And the Teton Dam’s reconstruction has never been ruled out.

Opposition? There’s plenty, and for lots of reasons. The river is home to a robust population of native Yellowstone cutthroat trout, and the fertile land within the Teton’s riparian zone is important habitat for mule deer, elk, upland game birds, and a host migratory waterfowl. Claims that new dam-building technology would prevent another disaster are countered by claims that dam tech isn’t all that different today than it was 50 years ago.

“I’m not sure just technology is going to solve all the problems that would prevent similar challenges to occur if (the dam) were rebuilt today,” said Lisa Ronald, northern Rockies associate conservation director for American Rivers told the Jackson Hole News & Guide in August 2025. She noted that the volcanic history of the region created porous conditions in the soil and the rocks of the area — those porous rocks were but one of many reasons the Teton Dam failed five decades ago. “And,” she said, “there were some decision-making failures.”

Rexburg in the wake of the Teton Dam flood (photo: waterarchives.org).

Half a century later

Fifty years later, the Teton River is an Idaho gem. Rolling across the upper Snake River plain and slicing through the volcanic basalt that’s common to the region, it’s a wonder to behold. The farms have returned, and the regional recovery is decades in the rearview mirror. The river, a tributary to the more heralded Henry’s Fork, is a stronghold for native Yellowstone cutthroat trout, and anglers in the know might actually favor this smaller river over the Henry’s Fork or the South Fork just a bit to the south. Dry-fly fishing for native cutthroats on the Teton is legendary.

Rexburg is no longer a Mormon farm town — today, the once-quaint community is home to BYU-Idaho, and more than 40,000 people call it home. Upstream from the old dam site, in Teton County, towns like Driggs and Victor serve as Jackson Hole overflow, and outdoor recreation, from hiking and skiing to fly fishing and ATV riding, brings visitors from all over to this once-hidden corner of the Gem State. Multi-million-dollar homes built in the shadow of the majestic Tetons continue to spring from the sage-covered prairie, and folks visiting Teton Valley might get the feeling that they’re not so much in rural Idaho as they are in a kitschy suburb of glitzy Jackson just over Teton Pass in Wyoming.

But make no mistake. The Teton flows through farm country, and water is still the lifeblood of this agrarian region. From higher-elevation hay fields at the base of the mountains to thousands upon thousands of acres of “amber waves of grain” and green fields of seed potatoes, the Teton Valley is one of Idaho’s most productive breadbaskets.

Add the skyrocketing populations in small cities like Rexburg and Rigby to the steady growth of Idaho Falls (which is home base to the Idaho National Laboratory, a federal nuclear research site located on the Arco Desert west of town) to the need to irrigate farm fields in the age climate uncertainty, and the water that flows down the Teton is really just on loan to the fish and the wildlife that depend on it.

So, it should come as no surprise that, in recent years, there have been legitimate discussions around trying to rebuild the dam that spanned the Teton River and flooded the basalt canyons behind it, albeit for just a short time. But, should something go horribly wrong (again), the consequences today, with many thousands of more people living and working downstream, would be much more devastating and much more costly.

Mr. and Mrs. Lauren Williams sit in the flooded Rexburg home of Mrs. Williams' mother, Thelma Williams, and view the damage caused by waters released by a collapsed dam. The floor is covered by mud and furnishings are ruined. The line showing the depth reached by the now-receded water is visible on the wall and drapes (photo: AP Wire / waterarchives.org).

Why did the dam fail?

The construction contract to build the Teton Dam was awarded to Morrison-Knudsen Company, which started work on the $100 million ($585 million in today’s dollars) project in February 1972. The dam was to have four purposes: hydro-power generation, recreation, irrigation, and the irony of all ironies — flood control.

As the dam’s construction proceeded, there were no glaring safety concerns. The project endured its share of delays over the course of its construction, which wasn’t terribly surprising for an undertaking of its scale. By November 1975, the “zoned earthfill embankment” that marked the Teton Dam was generally complete. Seven months later, the Teton River would roar through 300-foot-high berm and inflict Biblical destruction on the land and people in its angry course.

According to the Association of State Dam Safety Officials, the failure of the Teton Dam was the result of a “series of design and construction-related deficiencies.” Much of the geology of eastern Idaho was formed when the volcano beneath present-day Yellowstone National Park erupted about 2 million years ago. The eruption was massive, and emptied a subsurface magma chamber and created a caldera that’s about the size of the state of Rhode Island. That magma eventually cooled and solidified, creating the porous bedrock of the region. When dam construction personnel decided to use some of this rock in the project, it was determined that the “permeable foundation material” would need to treated using a process called slush grouting that was supposed to fill in the porous holes and make the volcanic rock impervious to the water it was designed to hold back. It turns out that only some of the rock used in the dam was property treated and some apparently wasn’t treated at all.

A review panel of dam construction experts inspected the site after it failed, and its members determined that inadequate treatment of the rock and the failure to treat the rock altogether as the dam got higher and higher was likely at the root of the dam’s collapse. “Working together or alone, either of these foundation design deficiencies would have provided conditions for internal erosion of the core,” a case study from the ASDSO concluded.

There were other contributing factors, however, including an astonishing omission of an external review of the project plans that might have uncovered the design issues. “Futhermore,” the ASDSO study reads, “the dam was not designed with any type of secondary defense against seepage and relied fully on the grout curtain and key trench.”

Scenes from the flood in Sugar City (photo: waterarchives.org).

A rebuild in the future?

In 2015, the U.S. Bureau of Reclamation and the Idaho Water Resource Board released the Henry’s Fork Basin Study, which examined the entire water tapestry in the Henry’s Fork Basin, of which the Teton is a significant part. In its entirety, the Henry’s Fork Basin contributes about 25 percent of the Upper Snake River Basin’s water, which not only flows down the Snake River and its tributaries, but also serves to recharge local aquifers and the vital Eastern Snake River Plain Aquifer. The latter might be the most important water source in the state for agricultural purposes.

The study, conducted under the Obama administration’s BOR, openly recognized that climate change was impacting water resources in the basin, both in the amount of precipitation the area receives, and in the form of the precipitation that falls on the region. “Climate change studies projected a shift in timing and increase in inflow volume to earlier in the year,” the study reads, which resulted in an increase in end-of-month storage earlier in the year and a greater need to use reservoir storage to provide irrigation water later in the summer months. For irrigation, reservoir management and ecological flow objectives, it was found that late season flow and reservoir objectives would be impacted the most by climate change, especially in the driest conditions.”

The take-away? The area needs more water storage to satisfy agricultural needs. And the BOR and IWRB offered a dozen alternatives to increasing water storage in the Henry’s Fork Basin. Reconstruction of the Teton Dam is one of the study’s alternatives. Not surprisingly, among stakeholders, it was among the least-popular of the alternatives. That said, of the 12 alternatives, a new reservoir behind a new dam on the Teton River would hold back more than 200,000 acre-feet of water, more than all the other alternatives combined.

In 2025, the Idaho State Senate, led by Sen. Kevin Cook, (R-Idaho Falls), passed Senate Memorial 101, urging the Department of Interior, the Bureau of Reclamation, the U.S. Army Corps of Engineers, Idaho Gov. Brad Little, the Idaho Water Resource Board, the Idaho Department of Water Resources, and Idaho’s federal congressional delegation to update all recent studies (including the 2015 Henry’s Fork Basin Study). The bill specifically noted that the Teton Dam failure was due to “design and operational decisions,” and that a reconstructed Teton Dam should be on the table for future discussion.

Last summer, Cook delivered the keynote address at a meeting hosted by the Eastern Idaho Water Rights Coalition and the Henry’s Fork Watershed Council, during which he claimed that lessons could be learned from the faulty design that doomed the original dam half a century ago.

“There are some people that are very, very worried about rebuilding the Teton Dam,” Cook said during that meeting. But, he said, technology has come a long way. “It broke 50 years ago. You didn’t have a microwave in your home. Many of you didn’t have a color TV.”

Remnants of the flood waters in Idaho Falls (photo: waterarchives.org).

Impacts beyond a second flood

Certainly, engineers behind any second run at building the dam would “go to school” on the first effort. Cook is probably right — today’s technology could likely prevent a second disaster. But there are other factors at play.

Rob Van Kirk, science and technology director at the Henry’s Fork Foundation, a regional conservation non-profit in Ashton, Idaho, put together a model simulating 25 years of Teton Dam operation. The model, he said, ranged from reservoir capacities of 20,000 acre-feet to 300,000 acre-feet.

“The model assumed water rights in Teton Reservoir were junior to existing rights, the only beneficial use allowed was managed aquifer recharge,” Van Kirk wrote in a prepared statement in the lead-up to the 50th anniversary of the disaster. “And the reservoir was managed to capture spring runoff and release available water for (managed aquifer recharge) during the winter. Results indicate that the maximum reservoir size that can be reliably filled is around 200,000 acre-feet and that the reservoir will store water available for new uses in only

around 50 percent of all years. On average, this new water is 12 percent of the state’s annual (managed aquifer recharge) goal, and the cost of storing it is 30 to 100 times the current value of (managed aquifer recharge) water.”

In other words, at the 2015 study’s estimated construction cost of well over $400 million, rebuilding Teton Dam is very likely not worth the water it would be designed to store.

“In addition to the high economic cost of building a dam that achieves its purpose only half the time, operations will result in reservoir and river hydrographs that will favor non-native fish over native cutthroat trout,” Van Kirk wrote.

In the age of climate change, the fate of one cutthroat subspecies might not seem like a metric worth mentioning. But the Yellowstone cutthroat trout native to the Henry’s Fork Basin really only has one dependable stronghold in the region — the Teton River. Throughout the rest of its native range, only about a quarter of it is actually occupied by the native cutthroat trout. Native cutthroats are very rare in the Henry’s Fork, and in the nearby South Fork, the native fish likely persist today because of efforts to keep non-native rainbow trout out of a handful of spawning tributaries. There are cutthroat populations in some of the smaller tributaries in the drainage, but there are just as many tributaries, if not more, that are home to non-native trout, like browns, brook trout, and rainbows.

The cutthroats in the Teton? They represent a rare asset in fisheries conservation — they’ve yet to be significantly impacted by hybridization by non-native rainbows. But that danger currently exists. Just last fall, Idaho Fish and Game worked to remove interloping rainbow trout from Badger Creek, a major tributary to the Teton River. IDFG, in a September 2025 news release, reported that Badger Creek’s lower five miles, prior to an October rotenone treatment, was home to 4,500 fish per mile — most of them rainbows.

“We have a good thing going here in the Teton River,” Will Stubblefield, the director of programs at Friends of the Teton River, told the News & Guide at that 2025 meeting. “A reservoir here would not be a good thing for that native [cutthroat trout] population.”