From fake eggs to faux brand-name handbags, China's enterprising counterfeiters are known for pushing the limits. And ever since Hong Kong installed a 54-foot yellow duck in its harbor, charming millions of fans, they've been especially busy, building a veritable brood of imitation yellow ducks that now dot cities across the mainland.

So far, the imitation ducks have sprung up in cities from Dongguan—which gave its duck a cartoonish twist, including a blue hair bow and long-lashed, wide eyes—to Xi'an, where the city's duck...