It's not easy being a mermaid. Just ask Rachel Smith, the head mermaid at Dive Bar, a plush lounge in downtown Sacramento. Every night, she and a dozen other professional mermaids perform elaborate routines to entertain patrons in a 40-foot aquarium populated by fish and filled with 7,500 gallons of saltwater. While Smith, who has been working at Dive Bar since it opened in January 2011, describes her job as a dream come true, she points out that being a mythical aquatic creature for a living has its challenges.

Rachel Smith, a professional mermaid, performing at Dive Bar Sacramento.

"It's really hard, which is something I don't think people fully understand, because we want it to look so effortless," she tells Fast Company. "Our legs are tied together, the fish are running into us, and it's dark. Our tails can weigh up to 35 pounds, but the saltwater makes us float, so we have another five to 10 pounds strapped between our legs; the movement is all from your core, so your abs are really working as you go through the tank."

As tough as the work is, there's been an explosion of professional mermaids, buoyed, you might say, by massive popular demand. Today, there are close to 1,000 full-time mermaids and mermen in the United States, according to the estimates of various experts I spoke with in the mer-community. These merfolk spend their days modeling in shimmering tails, performing for audiences in underwater tanks, and delighting children by making surprise appearances at their pool parties. Interested in booking a mermaid for your event? You can find one near you on the MerDirectory. Over the past five years, mermaid conferences have sprung up across the country, attracting hundreds of these performers: NC Merfest, which took place in January, was attended by 650 merfolk (and a sprinkling of pirates, for good measure).

The mermaid economy is is positively booming. It's been cultivated, in part, by the flurry of companies that create fish tails for children and adults to wear when they go swimming, allowing them to live out their dream of being a mermaid. Fin Fun, one of the largest brands on the market, says it currently sells 50,000 tails a month, while Mertailor can create elaborate custom-made tails for professional mermaids in a matter of days.

There are now mermaid exercise classes that allow you to work your core in the water. And out of the water, mermaid paraphernalia is flying off the shelves of toy stores and stationery shops. The buyers at Paper Source, for instance, told Fast Company they are stocking up on mermaid art prints, birthday party invitations, rubber stamps, and cards to cater to heightened demand.

Interest in mermaids is certainly not new. George Karpaty, the owner of Dive Bar, took a page out of the swimming shows that were all the rage in the 1950s when he was designing his mermaid-themed lounge. He was inspired by things like Weeki Wachee Springs, a Florida Gulf attraction that opened in 1947, where visitors watch mermaids perform (perhaps a more humane option than paying to see captive orcas).

Rachel Smith says that new Dive Bar patrons often don't know what to expect. "They wonder if it's a topless bar," she says. But the shows are actually very tame. The mermaid performers do tricks underwater, sometimes with props: they brush their hair with "dinglehoppers" (forks), right out of Disney's The Little Mermaid; they use bubble rings to draw hearts in the water; mermaid Stephanie even flips bottles under water in a bartender act. "I hope people who go in with licentious ideas about what they are going to see in the tank come away feeling a bit mesmerized and mollified," Smith says. "I want them to think, 'That wasn't what I was expecting, but it was really beautiful.'"

Smith and the three other original mermaids at Dive Bar were trained by L.A.-based Linden Wolbert, who is something of a mermaid pioneer. She began her career as a professional mermaid a decade ago when mermaid performers were still fairly rare. Having spent her life obsessed with the water, Wolbert decided to take a risk in 2005, after college, and pursue a career as a full-time mermaid. She moved back into her parents' home as she developed a client base and worked for seven months with special-effects artists to craft a silicone tail. "This was before there was anything mermaid-y on the market," Wolbert says. "It wasn't really a trend at all: I was just making up what I thought was a cool job."

Linden Wolbert, who's been a professional mermaid for about a decade.

But before long, Wolbert found herself in demand. She was asked to perform at parties, weddings, resorts, and hotels. Now, on an average weekend, she's performing at several children's birthday parties. She goes through a lot of effort to preserve the illusion that she is a genuine mermaid, ensuring that no children see her without her tail on. "I protect the realness of my identity fiercely," she says. "To the kids, it's real."

While she doesn't discuss her hourly fees publicly, the going rate is about $250 an hour for a children's event. Depending on the scale of the event and the size of the audience, professional mermaids can earn much more. For instance, since Wolbert is based in L.A., she's developed a client base of celebrities like Jessica Alba, Justin Timberlake, and Shia LeBeouf, who hire her to entertain guests at parties. Besides performing, Wolbert's career also involves underwater modeling, consulting for underwater photo shoots, and advising others—like the mermaids at Dive Bar—who are interested in learning her technique. She even has her own YouTube series called Mermaid Minute.

As someone who has tracked mermaid culture for about a decade, Wolbert says that fascination with mermaids has always been there under the surface, bubbling up every so often with big pop culture hits like the 1989 Disney movie The Little Mermaid or the sudden influx of YA novels about mermaids, like 2010's Forgive My Fins or 2012's The Syrena Legacy series. In 2012, celebrities like Katy Perry and Lady Gaga contributed to the trend by posting pictures of themselves dressed like mermaids. But Wolbert believes that there has been a real spike in the mermaid economy over the last five years as mermaid-focused businesses—like bars, performers, and tail makers—have sprung up to meet and fuel demand.

Take for instance Fin Fun, which launched in 2010 and creates mermaid tails for little girls. Fin Fun is an unlikely success story: the family-owned business started in Idaho, when grandmother Karen Browning decided to craft a functional mermaid tail for her granddaughter. After she created a successful prototype, she thought there could be a market for the product. Her children, several of whom worked at Fortune 500 companies, thought the idea was batty. "Creating a mermaid tail sounded like trouble to me," Eric Browning, Karen's son, admits.

Besides performing at parties, professional mermaid Linden Wolbert often models for underwater shoots.

But he was wrong. Karen put the tails up on eBay and began to sell them by the dozen. By 2012, Eric, who had spent his career in executive roles at Oracle, Micron Electronics, and Ancestry.com, decided to join the family business as CEO. Since then, growth has been exponential. Last month, the company sold 50,000 mermaid tails, which cost a little over $100, and sales appear to be growing. Eric Browning has focused heavily on improving and patenting the tails' design, while also creating massive amounts of content for children—from games to videos to stories—to help them immerse themselves in the world of mermaids. "It's more than just selling product," he says. "We sell an adventure and an experience. We want to create a place that parents can trust their kids to be."

Safety is one of Fin Fun's biggest challenges, since the brand is catering specifically to young children: for weak swimmers, having their legs bound together in a monofin could be a potential drowning risk. In Canada, for instance, the safety of mermaid tails came up earlier this summer at the annual Alberta Association of Recreation Facility Personnel conference. While Fin Fun was not specifically called out, Eric Browning provided a detailed response about how his company's fins can be safely used: children should be able to swim continuously for 25 meters, tread water for two minutes, and even then, be supervised by adults at all times. While Fin Fun is continuously working to improve safety features, the fins are likely to be an ongoing concern for parents.

Kids aren't the only ones buying into the mermaid trend. A company called Mertailor has been creating customized silicone and latex mermaid tails since 2006, and has become a go-to place for people who are interested in becoming professional mermaids. The company's founder, Eric Ducharme, began by supplying mermaid shows and stylists who wanted to include a mermaid in photo shoots for ads and magazines. But over the years, everyday consumers obsessed with mermaids have asked Mertailor to create tails for them to bring to the pool or the ocean. Tails can run anywhere from $500 to $25,000 and beyond. The company is about to launch a line of non-customized tails at the lower price point of $100, which will allow it to compete more directly with Fin Fun.

Mertailor designed the tails for this advertisement by NuMe.

A second wave of businesses cater to people who have bought mermaid tails. "Mermaid schools" have opened up around the world, from Hawaii to Spain to the Philippines, where people can learn to swim in a mermaid tail while also getting a solid workout. There's an International Mermaid Swimming Instructor's Association that provides a list of instructors and schools who are available to teach classes. Interest in mermaid swimming appears to be growing, with new courses popping up on a monthly basis. JodiAnn Stevenson, for instance, has just launched Mermaid Fitness, a Michigan-based company that offers classes that are designed to strengthen the core. "Most people are drawn to it because of the novelty of doing something really silly and crazy and fun," Stevenson says. "A lot of people just really love mermaids."