Less than a decade ago, Bacheng was an obscure lake town, according to crab harvesters and restaurant owners. Now, with superhighways putting Shanghai an hour away, the area is mobbed through the fall. Trains, buses and cars from east China, and tours from Japan and Hong Kong, throng lakefront shops and floating boats.

"What was here seven years ago?" asks Kang Luo, a parking lot attendant born in Bacheng who carries a walkie-talkie. "Nothing! Today, I've let in almost 3,000 cars."

Girls with crab brochures accost vehicles with out-of-town plates at intersections. Neon glows on the quiet lake at night above restaurants with names like "Pearl Crab," "Every Day Happy Crab," and "Purple Crab." Tourists emerge from shops with boxes of live crabs packed in grass matting.

"People are really loving the hairy crab. They drive hours to find the best places," says a Shanghai traveler in the construction business, whose wallet sports crab-house business cards.

"I've had crab three days in a row, and I've come back again today," says Steven Li, a Singaporean who lives in Shanghai, and whose Porsche sits in the parking lot. "My girlfriend loves coming here. It is an event that we can repeat."

Unsurprisingly, the five-year crab craze has spawned a huge industry of fakes. Perhaps only one of every 70 crabs sold as Yangcheng is the genuine article, studies show. The local Jiangsu area is pockmarked with similar lakes, and the crab species is virtually the same, so impostors are easy to produce. The difference in taste is roughly akin to that between cage-raised and free-range chickens. The meat is grainier and sweeter. Yet without tests, even many Yangcheng residents can't always judge a crab by its spiny cover.

Four years ago, to try to block the fakery, Yangcheng fisheries started to lightly torch the crab with a laser ID number as they were pulled from the waters. But that practice has been abandoned. The laser numbers proved easy to duplicate. A $5 stand-in from a nearby lake can become a $35 Yangcheng crab in seconds.

"Crab pirates easily duplicated the laser numbers," says De Zhou Zhu, owner of Big Brother De's crab house on the lake, which sports a photo of former President Jiang Zemin eating there.

"I've stopped shipping the crabs, and only sell from this shop," Mr. De adds. "My agents in Hong Kong and Singapore were starting to sell fakes in my name."

"Even if you come to Yangcheng, if you don't have the right contacts, you may buy fake crabs," says Wang Wen Long, owner of Wang Fu's Delight Crab on the lake.