To ride down the Columbia River as the John Day Dam’s wall of concrete slowly fills the view from a tugboat is to see what the country’s largest network of energy-producing dams created through five decades of 20th-century ambition, investment and hubris.

Nearly half of the nation’s hydropower electricity comes from more than 250 hydropower dams that were built on the Columbia and its tributaries — a vast and complex arc of industry and technology that touches tens of millions of lives across the West every day.

Google taps the river’s energy to power a data center 90 minutes east of Portland, Ore. — drawn there by some of the cheapest, most environmentally friendly electricity in the nation. Farmers farther upriver in Washington State pump irrigation water into alfalfa fields — with both the water and the electricity supplied by a dam. The Space Needle in Seattle uses Columbia River electricity to slowly spin tourists in its sky-view restaurant. High-voltage transmission lines shoot south to California.

Now, the Trump administration has proposed rethinking the entire system, with a plan to sell the transmission network of wires and substations owned by the Bonneville Power Administration, a federal agency that distributes most of the Columbia basin’s output, to private buyers.

The idea is part of a package of proposals that would transform much of the infrastructure in the United States to a mixture of public and private partnerships, lowering costs to taxpayers and improving efficiency, administration officials said. Assets of two other big public power operators, based in Colorado and Oklahoma, would be sold, too, if Congress approves the measure.

Debates about government and its role in land and environmental policy are always highly charged. But perhaps nowhere could the proposed changes have a more significant impact than along the great river of the West — fourth largest by volume in North America, more than 10 times that of the Hudson. Privatization would transform a government service that requires equal standards across a vast territory — from large cities to tiny hamlets — into a private operation seeking maximum returns to investors.

Wringing profits from a system that has provided electricity at cost would inevitably raise prices, critics of the idea said, while supporters envision a streamlined grid open to innovations that government managers cannot imagine.

CANADA ANNUAL ENERGY OUTPUT In average megawatts Chief Joseph Dam 1,321 megawatts 2,000 1,000 250 Kalispell DAM OWNERSHIP Columbia R. Seattle Polson Government Coeur d'Alene Spokane Private Wenatchee Olympia Grand Coulee Dam 2,372 megawatts MONTANA WASHINGTON Missoula Yakima Astoria Lewiston Richland Longview Walla Walla Butte Bozeman IDAHO Columbia R. Portland PACIFIC OCEAN Columbia river basin John Day Dam 1,147 megawatts Salem Corvallis Brownlee Dam 340 megawatts Eugene Bend Ontario Boise Idaho Falls OREGON Snake R. WYOMING Burley Twin Falls CALIFORNIA NEVADA UTAH Salt Lake City CANADA ANNUAL ENERGY OUTPUT In average megawatts Chief Joseph Dam 1,321 megawatts 2,000 Columbia R. 1,000 Kalispell 250 Coeur d'Alene Spokane Seattle DAM OWNERSHIP Government Olympia Grand Coulee Dam 2,372 megawatts MONT. Private Missoula WASH. Astoria Longview Richland Walla Walla Butte Bozeman Portland Columbia R. Columbia river basin Salem John Day Dam 1,147 megawatts PACIFIC OCEAN Brownlee Dam 340 megawatts Eugene Bend Ontario Idaho Falls Boise ORE. IDAHO Snake R. WYO. Twin Falls CALIF. NEV. UTAH Salt Lake City CANADA ANNUAL ENERGY OUTPUT In average megawatts Chief Joseph Dam 1,321 megawatts Columbia R. Kalispell 2,000 Coeur d'Alene Seattle 250 Grand Coulee Dam 2,372 megawatts MONT. DAM OWNERSHIP Missoula WASH. Government Richland Private Butte Columbia river basin Portland Columbia R. Bozeman Salem John Day Dam 1,147 megawatts WYO. Brownlee Dam 340 megawatts Eugene Bend Ontario Idaho Falls Boise IDAHO ORE. Snake R. Pocatello Twin Falls CALIF. NEV. UTAH Salt Lake City ANNUAL ENERGY OUTPUT In average megawatts CANADA Chief Joseph Dam 1,321 megawatts Columbia R. Kalispell 2,000 MONT. Coeur d'Alene Seattle 250 Grand Coulee Dam 2,372 megawatts Missoula DAM OWNERSHIP Government Richland Butte Private Columbia R. IDAHO John Day Dam 1,147 megawatts Portland Bozeman Salem Columbia river basin WYO. Brownlee Dam 340 megawatts Eugene Ontario Bend Idaho Falls Boise ORE. Pocatello Snake R. Twin Falls CALIF. NEV. UTAH ANNUAL ENERGY OUTPUT In average megawatts DAM OWNERSHIP Government Private 2,000 250 WASH. Grand Coulee Dam 2,372 megawatts Seattle Columbia R. MONT. Portland Columbia river basin John Day Dam 1,147 megawatts Brownlee Dam 340 megawatts Snake R. ORE. IDAHO UTAH CALIF. NEV.

A New York Times reporter and photographer went down the river in June, bunking with a five-man tug crew over 30 hours as workers cooked their meals, rested between shifts and transited through four dams and locks. We were looking for the interconnections of electricity and navigation, private industry and government management, engineering and biology, and what is at stake in this new energy debate.

Those stakes start with the scale. Grand Coulee alone, the biggest dam on the river, ships power to 10 states and creates enough electricity to power all the households in Missouri for a year. The 12 million cubic yards of concrete it contains is enough to build a highway from Seattle to Miami.

The possible fate of that system is raising alarms for some, and questions for almost everyone whose life connects to the river.

“The uncertainty is the biggest thing of all: How would it work?” Terry Oxley, the captain of the tugboat, the Crown Point, said as he gazed out over the water, hands flicking the controls with practiced aplomb. Mr. Oxley, 63, has worked the tugs for 39 years.

“I guess I want more input,” he added. “Who’s going to control it? Who’s going to have the say so? When are they going to release the water, the flood control, the spill patterns for the fish? It’s such a big deal, and it’s all intertwined.”

Approaching the Locks at McNary Dam

UMATILLA, Ore. — It was just before 2 a.m., and the fierce winds that were gusting to 50 miles per hour earlier in Riley Wyatt’s shift on the Crown Point had eased. But Mr. Wyatt was taking no chances.

“No room for error,” he said as he slowed the tug to a crawl approaching the locks at McNary Dam, 200 miles upriver from Portland. The Crown Point had picked up a 14,000-ton load in Pasco, Wash. — three barges of wheat and one empty fuel tanker — before taking it to Vancouver, Wash. Crew members were posted on the four barges pushed by the tug, reporting back by radio as the distance to the walls of the lock narrowed to inches.

“We’re pushing a lot of energy,” Mr. Wyatt, 41, said. “We hit something even at one mile an hour, it makes a big boom.”

The dams and the locks that make up Mr. Wyatt’s workplace were built by engineers who utterly transformed — or destroyed, depending on your point of view — what had been one of the wildest rivers in America.

From the mid-1930s, when construction began on the Grand Coulee and Bonneville Dams, through the mid-1970s, when the last major dams were completed on two Columbia tributaries, builders set the standard for public works as tools of economic development. Coulee and Bonneville employed about 9,000 construction workers, and Coulee alone cost about $5.5 billion in today’s inflation-adjusted dollars.

The dams blocked the river’s flow, creating a network of placid reservoirs. Irrigation canals spidered out, fostering one of the nation’s richest breadbaskets in the orchards and vineyards of Washington. Mammoth turbines powered the airplane factories of Puget Sound and the boom of postwar California.

But development came with costs. Native American tribes saw their lands destroyed. Salmon stocks, already decimated by overfishing, were driven into further peril by rising water temperatures and dams that made it harder for fish to move up- and downriver in their ancient cycles of reproduction.

Native American tribal leaders said that the old river would never come back, but that the federal government was now bound, through court decisions and treaties, to work with tribes going forward.

“Obligations are tied to the federal relationship,” said Jaime A. Pinkham, the executive director of the Columbia River Inter-Tribal Fish Commission and a member of the Nez Percé tribe. “When you privatize, what happens to the voice of the Indian people?”

At the Confluence of the Columbia and Snake Rivers

PASCO, Wash. — While the idea of selling some or all of what the federal government built here is not new — President Ronald Reagan floated the idea in the early 1980s — it’s a much different debate this time. Reagan proposed a clean-sweep sale of public power into private hands, from dams to wires.

The new proposal would keep the electricity-making in government control, while spinning off the system of getting that electricity to market. Partial privatization would require complex new contracts delineating the responsibilities of the public and private partners. And what feeds into that system has grown more complicated since the 1980s as well, with a huge growth of new sources like wind and solar.

But some energy experts who back the Trump plan said that despite the thorny details, a powerful word could resonate in Congress: fairness. Low prices in a nonprofit system have been a huge boost to economic growth in this corner of the nation.

“We should have a debate about why some minority of Americans get subsidized power and others don’t,” said Chris Edwards, an economist at the Cato Institute.

Government brought electricity to remote rural towns starting in the 1930s, and people there haven’t forgotten.

John Friederichs, manager of the Ferry County Public Utility District in northeast Washington, said a shift in focus to larger population centers, because that’s where the profits are, could leave tiny markets like his — about 7,500 people — out in the cold with lower priority for maintenance or repairs.

“When you have something that works, having caution about changing it seems reasonable,” he said.

Technology Giants Find a Home

THE DALLES, Ore. — Powerful new economic voices have emerged since the last big grid debate, as companies like Google, Microsoft and Amazon invested billions of dollars in building data centers for the internet in Bonneville’s territory. Those new customers already inject greater private market forces into the system as they negotiate contracts for their energy needs.

In cities like The Dalles, 90 minutes east of Portland, Google has become a community patron of sorts, too, residents said, with grants to libraries and schools.

“Google has been good for us,” said the city’s mayor, Steve Lawrence. “They’re a full partner.”

But discontent with the old system of public power has grown in some places, bolstering the political chances of privatization. In Sherman County, Ore., for example, southeast of The Dalles, President Trump won 72 percent of the vote, and critics of Bonneville Power seem just about as prevalent because of how grid operators have incorporated, or not, the new rising force of wind energy into a system dominated by hydropower.

Wind revenue is paying for the expansion of the Sherman County Courthouse and the annual dividend checks that property owners in the county have received. Kathy McCullough said kilowatt dollars had become important to her family farm’s budget, hedging against fluctuations in wheat prices.

Bonneville power managers repeatedly hit the off switch on wind this year in Sherman — curtailment is the term — because too much water was coming through the dams after last winter’s huge snowpack, which in turn meant more hydroelectricity flowing through the grid.

More curtailments have happened this year than ever before, according to the Northwest Power and Conservation Council, as Bonneville managers struggled to keep the system in balance. A change in ownership, supporters of the Trump plan in Sherman said, could be good for them in opening new opportunities for wind power sales.

“The B.P.A. does a terrible job,” Ms. McCullough said in reference to Bonneville Power. “I don’t know that privatizing would be bad at all.”

Some environmental groups also chafe against Bonneville, for the access fees that they said could discourage wind development and the system’s difficulties in juggling all of the new energy sources.

But Doug Howell, a spokesman for the Sierra Club in Washington State, said privatizing would not solve those problems — and could in fact make them worse.

“The answer is not privatizing,” he said. “It’s integration.”

One longtime veteran of river management said the new argument over the power system’s future just reprised an old question: Whom does the Columbia belong to?

“Everybody takes a piece of the Columbia,” said Tom Eckman, a senior adviser to the Northwest Power and Conservation Council. “And then they have to collaborate and cooperate over its resources, or fight over them.”