Business is so good for SEI Manufacturing in Cromwell, Ind., that there’s only one thing preventing explosive growth: a shortage of workers. “I could double my revenue if I could get the workers,” says Nathan Scherer, the 37-year-old owner of the company, which makes marine components. “It frustrates me. I never would have thought the biggest barrier to my success would be an inability to get workers.”

President Trump has promised to “bring back” manufacturing jobs he claims have been shipped to countries like China and Mexico, and revive fading industries such as coal and steel. But in many pockets of the country, the problem isn’t shuttered factories or abandoned mines but humming businesses that can’t find the staffers they need.

The Labor Department reports nearly 6 million jobs open nationwide, close to the highest level in the 17 years the government has been gathering such data. The unemployment rate, at 4.4%, is below the level many economists consider “full employment,” or the rate at which employers must start boosting wages to lure the workers they need.

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There are still about 8 million Americans who are unemployed, underemployed or drifting in and out of the labor force. Perhaps 10 million other working-age adults have dropped out of the labor force and given up looking for a job. That’s a real problem, but it doesn’t mean there aren’t enough jobs in the country. It means the jobs aren’t located where the jobless live, or the available jobs require skills the jobless don’t have. It’s also possible some people who aren’t working simply don’t want the jobs that are available.

Trucking companies, for instance, are short about 50,000 drivers, according to Bob Costello, chief economist for the American Trucking Association. It’s obviously demanding work that requires being away from home for 7 to 10 days at a stretch. But pay has been rising, Costello says, with a typical driver able to earn $50,000 t0 $70,000 a year. The driver shortage has made companies more flexible, and willing to let drivers make their own schedules, when possible. And the nature of the job lets drivers live in low-cost areas of their choosing, with the south and Midwest being best, logistically. Still, the driver shortage is expected to intensify rather than ease, and despite the hype, self-driving trucks that could help solve the problem are probably still decades away.

Nathan Scherer, owner of SEI Manufacturing, right, with Andy Cripe, owner of Polar Kraft Boats. Both Indiana companies are struggling to find needed workers. More

There are many anecdotal reports of labor shortages across the country. Farmers in California report that seasonal foreign workers aren’t showing up the way they used to—and neither are Americans happy to take the work foreigners are leaving behind, even though pay is approaching $15 per hour, or more. A tech and manufacturing boom in Utah and Colorado has pushed the unemployment rate more than a full percentage point below the national average in those states, and led to labor shortages in construction, health care and other sectors. In North Carolina, builders can’t erect enough homes to meet demand because they can’t find the workers. Home prices will rise, contractors say, as they’re forced to pay more to draw people to job sites.

Job-search site Indeed says these are the top 10 cities for job growth:

And these are the worst 10 cities, where job growth is actually negative:

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