Cultured freshwater pearls were once easy to spot. They typically lacked the luster their saltwater rival Akoya pearls had.
Akoya pearls are produced in saltwater in Japan. Mikimoto may come to mind. Akoya pearls are most often nucleated with a shell bead and mantle tissue that causes the mollusk to excrete layers of nacre around the bead, creating a round pearl.
Recently the Chinese found a way to rival this process successfully nucleating freshwater mollusks. These pearls are hard, at first glance, to distinguish from Akoyas. The type of blemishes produced differs a bit from the Akoya.
These Chinese pearls are being marketed as “freshwater Akoya pearls”. I personally find them beautiful. Because they are so similar to their Japanese rival, and about half the price or better, I’ve chosen to use them in many of my projects.