KLAMATH FALLS, Ore. — Through the marshlands along the Oregon-California border, the federal government a century ago carved a whole new landscape, draining lakes and channeling rivers to build a farming economy that now supplies alfalfa for dairy cows and potatoes for Frito-Lay chips.

The drawdowns needed to cover the croplands and the impacts on local fish nearing extinction have long been a point of conflict at the Klamath Project, but this year’s historic drought has heightened the stakes, with salmon dying en masse and Oregon’s largest lake draining below critical thresholds for managing fish survival. Hoping to limit the carnage, federal officials have shut the gates that feed the project’s sprawling irrigation system, telling farmers the water that has flowed every year since 1907 will not be available.

Some farmers, furious about water rights and fearing financial ruin, are already organizing a resistance. “Tell Pharaoh let our water feed the Earth,” said a sign erected near the nearly dry irrigation canal that would usually be flowing with water from Upper Klamath Lake in southern Oregon.

The brewing battle over the century-old Klamath Project is an early window into the water shortfalls that are likely to spread across the West as a widespread drought, associated with a warming climate, parches watersheds throughout the region.

In Nevada, water levels have dropped so drastically in Lake Mead that officials are preparing for a serious shortage that could prompt major reductions in Colorado River water deliveries next year. In California, Gov. Gavin Newsom has placed 41 counties under a state of emergency.

While drought consumed much of the West last year, setting the stage for an extensive wildfire season, the conditions this spring are far worse than a year ago. More than half of the West faces “extreme” drought conditions, according to the U.S. Drought Monitor, including wide areas of California and Oregon. Scientists have said the region may be going through the worst drought period in centuries.

Here in Oregon, conservationists, Native American tribes, government agencies and irrigators are squaring off, and local leaders fear that generations of tensions could escalate in volatile new ways.

“There are folks on both sides that would really like to throw down and take things in an ugly direction,” said Clayton Dumont, a member of the Klamath Tribal Council. “I hope it doesn’t happen, but it’s a possibility.”

Some landowners have openly talked about breaching the fence surrounding the dam property and forcing open the irrigation gates. Already, they have purchased property adjacent to the head gates and staged protests there. Ammon Bundy, who led an armed takeover of an Oregon wildlife refuge in 2016, said he was ready to bring in allies to help keep the gates open, saying that people need to be prepared to use force to protect their rights even if law enforcement arrives to stop them.

“Who cares if there is violence? At least something will be worked out,” Mr. Bundy said in an interview, ridiculing those not prepared to fight for the nation’s food supply. “‘Oh, we don’t want violence, we’ll just starve to death.’ Heaven forbid we talk about violence.”

The region has a deep history rooted in violence and racial division. In 1846, U.S. War Department surveyors, led by John C. Frémont and Kit Carson, slaughtered more than a dozen Native Americans on the shores of Klamath Lake. The Klamath Tribes eventually signed a treaty surrendering some 20 million acres of their historic lands in exchange for a reservation along Upper Klamath Lake and the perpetual right to hunt and fish.

For the United States, the Klamath Project became a keystone for settling and developing the region. Homestead opportunities for veterans after the two world wars helped to stimulate the economy and to build a new kind of community.

In 1954, Congress moved to terminate recognition of the Klamath Tribes, which held lucrative timberlands, and authorized the sale of tribal lands.

And the government’s guarantee to the Klamath Tribes that they would at least be able to continue fishing ran into trouble decades ago, when populations of native sucker fish — known to the tribes as C’waam and Koptu — along with coho salmon farther downriver slipped into a perilous decline, prompting mandatory protections under the Endangered Species Act.

During a drought in 2001, the federal Bureau of Reclamation initially planned for the first time to fully cut off water for farmers over the summer. That order spurred an uprising of farmers and ranchers who used saws, torches and crowbars to breach the facilities and open the canal head gates.

U.S. Marshals eventually stepped in to protect the gates, and the Bureau of Reclamation later released some water to help farmers.

Later that year, three men were charged with going on a racist shooting spree through the town where the Klamath Tribes have their offices.

Now some in the basin are worried that the unresolved divisions are poised to erupt again.

“These are not things that are going to get better if climate change continues to give us more uncertainty and less reliable supplies of water,” said William Jaeger, an economics professor at Oregon State University who specializes in environmental, resource and agricultural policy issues. He said the drought conditions that emerged in recent decades, in part fueled by declines in snowpack, were likely to happen again in the future — and there needed to be a recognition that the Klamath Basin was overcommitted in its water obligations.

This year shows how critical the shortage is already: Even with farmers cut out of the water supply, fish are suffering.

Lake levels fell below the minimum thresholds set by federal scientists, prompting litigation and spurring fears that algae blooms this summer could devastate the imperiled fish populations above the dam; tribal researchers say insufficient flushing downstream from the dam has allowed parasites to flourish.

Already this year, juvenile salmon are turning up dead with parasitic infections. Michael Belchik, a senior water policy analyst at the Yurok Tribe, said the die-off could end up being the worst on record.

“This is really catastrophic,” Mr. Belchik said. “We are starting to talk about the ‘extinction’ word around here.”

Tricia Hill, who grows potatoes, onions, mint and other crops across some 14,000 acres in the basin, much of it within the Klamath Project, said the focus on managing individual fish species under threat had failed. Despite 20 years of efforts, including water restrictions for farmers, the fish are still in decline. And, Ms. Hill said, the economy is at a standstill and families are struggling.

“It feels really bad to see this much pain and not think that it’s doing a darn bit of good,” Ms. Hill said, standing next to a sprawling patch of desolate land on a family farm that is now in its second season with nothing but scrubby cover crops designed to keep the soil from blowing away. “This is awful — I have cried a ridiculous amount this year,” she said.

Also cut off from water supplies this year are several wildlife refuges that are home to 25 at-risk species of birds and fish.

Farmers generally have been split on how aggressively to push back against this year’s water shut-off. Ms. Hill said she disliked the idea of forcing open the gates, saying that option would do little to help. Other farmers have also called for ratcheting back the threats.

But on Thursday night, about 100 people gathered under a large tent next to the head gates on property bought recently by two farmers, Dan Nielsen and Grant Knoll, who say they have a legal entitlement to the water behind the gates in Upper Klamath Lake under state water law. They contend that the federal government’s shut-off is a violation of state and federal law and the U.S. Constitution.

Tribes and irrigators have each notched victories in court over water rights, and the legal cases are continuing.

At the event, organized by local activists in Mr. Bundy’s network, speakers talked about the need to take back their rights. Some floated unfounded conspiracy theories, linking the water crisis to George Soros, Bill Gates or the United Nations. A Betsy Ross flag flew above the tent while a poster inside featured a quote about freedom attributed to LaVoy Finicum, who was killed by federal agents during the standoff that Mr. Bundy led in 2016. Mr. Bundy faced federal charges for his role in the standoff but was acquitted by a jury.

The local sheriff, Chris Kaber, told the crowd that he attended because he had personal friends in the group but planned to remain publicly neutral in order to keep the peace.

Mr. Knoll told the group that the best way to open the head gates would be for the local irrigation district — on whose board he sits — to do it, in defiance of the Bureau of Reclamation. But he said his fellow board members seemed unwilling to take that step.

“The next way to open it is you know what,” Mr. Knoll told the crowd. “And that’s where all the fun begins.”

Facing a similar standoff two decades ago, in 2001, the federal government relented with a limited delivery of water to farmers, but there was no sign that agencies, facing an already depleted lake, would budge this time. An initial plan to provide a small water allocation to farmers was canceled when conditions worsened.

Ms. Hill said she expected that some farmers would be unable to make their mortgage payments this year. Some may file for bankruptcy. Ms. Hill said she expected that her operation would survive this year, but as a fourth-generation farmer, she had begun to wonder whether her daughters would be able to follow in her footsteps.

“Farmers, by their nature, are optimists,” she said. “I have to hope, but I’m definitely worried.”