Maine has a lot of lobsters. It also has a lot of older people, ones who are less and less willing and able to catch, clean and sell the crustaceans that make up a $1 billion industry for the state. Companies are turning to foreign-born workers to bridge the divide.

“Folks born in Maine are generally not looking for manufacturing work, especially in food manufacturing,” said Ben Conniff, a founder of Luke’s Lobster, explaining that the firm’s lobster processing plant has been staffed mostly by immigrants since it opened in 2013, and that foreign-born workers help keep “the natural resources economy going.”

Maine has the oldest population of any U.S. state, with a median age of 45.1. As America overall ages, the state offers a preview of what that could look like economically — and the critical role that immigrants are likely to play in filling the labor market holes that will be created as native-born workers retire.

Nationally, immigration is expected to become an increasingly critical source of new workers and economic vibrancy in the coming decades.

It’s a silver lining at a time when huge immigrant flows that started in 2022 are straining state and local resources across the country and drawing political backlash. While the influx may pose near-term challenges, it is also boosting the American economy’s potential. Employers today are managing to hire rapidly partly because of the incoming labor supply. The Congressional Budget Office has already revised up both its population and its economic growth projections for the next decade in light of the wave of newcomers.

In Maine, companies are already beginning to look to immigrants to fill labor force gaps on factory floors and in skilled trades alike as native-born employees either leave the work force or barrel toward retirement.

State legislators are working to create an Office of New Americans, an effort to attract and integrate immigrants into the work force, for instance. Private companies are also focused on the issue. The Luke’s Lobster founders started an initiative called Lift All Boats in 2022 to supplement and diversify the fast-aging lobster fishing industry. It aims to teach minorities and other industry outsiders how to lobster and how to work their way through the extensive and complex licensing process, and about half of the participants have been foreign-born.

They included Chadai Gatembo, 18, who came to Maine two years ago from the Democratic Republic of Congo. Mr. Gatembo trekked into the United States from Central America, spent two weeks in a Texas detention center and then followed others who were originally from Congo to Maine. He lived in a youth shelter for a time, but now resides with foster parents, has learned English, has been approved for work authorization and is about to graduate from high school.

Mr. Gatembo would like to go to college, but he also enjoyed learning to lobster last summer. He is planning to do it again this year, entertaining the possibility of one day becoming a full-fledged lobsterman.

“Every immigrant, people from different countries, moved here looking for opportunities,” Mr. Gatembo said. “I have a lot of interests — lobster is one of them.”

A smaller share of Maine’s population is foreign-born than in the country as a whole, but the state is seeing a jump in immigration as refugees and other new entrants pour in.

That echoes a trend playing out nationally. The Congressional Budget Office estimates that the United States added 3.3 million immigrants last year and will add another 3.3 million in 2024, up sharply from the 900,000 that was typical in the years leading up to the pandemic.

One-third to half of last year’s wave of immigrants came in through legal channels, with work visas or green cards, according to a Goldman Sachs analysis. But a jump in unauthorized immigrants entering the country has also been behind the surge, the economists estimate.

Many recent immigrants have concentrated in certain cities, often to be near other immigrants or in some cases because they were bused there by the Texas governor, Greg Abbott, after crossing the border. Miami, Denver, Chicago and New York have all been big recipients of newcomers.

In that sense, today’s immigration is not economically ideal. As they resettle in clusters, migrants are not necessarily ending up in the places that most need their labor. And the fact that many are not authorized to work can make it harder for them to fit seamlessly into the labor market.

Adriana Hernandez, 24, a mother of four from Caracas, Venezuela, is living with her family in a one-bedroom apartment in Aurora, Colo. After journeying through the Darién Gap and crossing the border in December, Ms. Hernandez and her family turned themselves in to immigration authorities in Texas and then traveled by bus to Colorado.

They have no work authorization as they wait for a judge to rule on their case, so Ms. Hernandez’s husband has turned to day labor to keep them housed and fed.

“Economically, I’m doing really badly, because we haven’t had the chance to get a work permit,” Ms. Hernandez said in Spanish.

It’s a common issue in the Denver area, where shelters were housing nearly 5,000 people at the peak early this year, said Jon Ewing, a spokesman with Denver Human Services. The city has helped about 1,600 people apply for work authorization, almost all successfully, as it tries to get immigrants on their feet so they do not overwhelm the local shelter options.

Most people who gain authorization are finding work fairly easily, Mr. Ewing said, with employers like carpenters and chefs eager for the influx of new workers.

Nationally, even with the barriers that prevent some immigrants from being hired, the huge recent inflow has been helping to bolster job growth and speed up the economy.

“I’m very confident that we would not have seen the employment gains we saw last year — and we certainly can’t sustain it — without immigration,” said Wendy Edelberg, the director of the Hamilton Project, an economic policy research group at the Brookings Institution.

The new supply of immigrants has allowed employers to hire at a rapid pace without overheating the labor market. And with more people earning and spending money, the economy has been insulated against the slowdown and even recession that many economists once saw as all but inevitable as the Federal Reserve raised interest rates in 2022 and 2023.

Ernie Tedeschi, a research scholar at Yale Law School, estimates that the labor force would have decreased by about 1.2 million people without immigration from 2019 to the end of 2023 because of population aging, but that immigration has instead allowed it to grow by two million.

Economists think the immigration wave could also improve America’s labor force demographics in the longer run even as the native-born population ages, with a greater share of the population in retirement with each year.

The nation’s aging could eventually lead to labor shortages in some industries — like the ones that have already started to surface in some of Maine’s business sectors — and it will mean that a smaller base of workers is paying taxes to support federal programs like Social Security and Medicare.

Immigrants tend to be younger than the native-born population, and are more likely to work and have higher fertility. That means that they can help to bolster the working-age population. Previous waves of immigration have already helped to keep the United States’ median age lower and its population growing more quickly than it otherwise would.

“Even influxes that were difficult and overwhelming at first, there were advantages on the other side of that,” Mr. Tedeschi said.

In fact, immigration is poised to become increasingly critical to America’s demographics. By 2042, the Congressional Budget Office estimates, all American population growth will be due to immigration, as deaths cancel out births among native-born people. And largely because immigration has picked up so much, the C.B.O. thinks that the U.S. adult population will be 7.4 million people larger in 2033 than it had previously expected.

Immigration could help reduce the federal deficit by boosting growth and increasing the working-age tax base, Ms. Edelberg said, though the impact on state and local finances is more complicated as they provide services like public schooling.

But there are a lot of uncertainties. For one thing, nobody knows how long today’s big immigration flows will last. Many are spurred by geopolitical instability, including economic crisis and crime in Venezuela, violence in Congo, and humanitarian crises across other parts of Africa and the Middle East.

The C.B.O. itself has based its projections on guesses: It has immigration trailing off through 2026 because it anticipates a slow reversion to normal, not because it is actually clear when or how quickly immigration will taper.

National policies could also reshape how many people are able to come to — and stay in — the United States.

The influx of immigrants has caused problems in many places as the surge in population overwhelms local support systems and leads to competition for a limited supply of housing. As that happens, immigration has become an increasingly critical political issue, surging to the top of the list of the nation’s most important problems in Gallup polling.

Former President Donald J. Trump, the presumptive Republican nominee, has warned of an immigrant-created crime wave. He has pledged to deport undocumented immigrants en masse if he wins the presidential election in November.

The Biden administration has used its executive authority to open a back door to allow thousands of migrants into the United States temporarily, while also taking steps to repair the legal refugee program. But as Democratic leaders have joined Republicans in criticizing President Biden over migration in recent months, he has embraced a more conservative tone, even pledging to “shut down” the border if Congress passed a bill empowering him to do so.

Politics are not the only wild card: The economy could also slow. If that happened, fewer immigrants might want to come to the United States, and those who did might struggle to find work.

Some economists fret that immigrants will compete against American workers for jobs, particularly those with lower skill levels, which could become a more pressing concern in a weaker employment market. But recent economic research has suggested that immigrants mostly compete with one another for work, since they tend to work in different roles from those of native-born Americans.

At the Luke’s Lobster processing plant in Saco, Maine, Mr. Conniff has often struggled to find enough help over the years, despite pay that starts at $16 per hour. But he has hired people like Chenda Chamreoun, 30, who came to the United States from Cambodia in 2013 and worked her way up from lobster cleaning to quality assurance supervisor as she learned English.

Now, she is in the process of starting her own catering business. Immigrants tend to be more entrepreneurial than the nation as a whole — another reason that they could make the American economy more innovative and productive as its population ages.

Ms. Chamreoun explained that the move to the United States was challenging, but that it had taught her how to realize goals. “You have more abilities than you think.”

J. Edward Moreno contributed reporting from New York, and Zolan Kanno-Youngs from Washington.