Freshwater pearls are common elements of modern pearl jewellery. They differ from natural, genuine pearls and fake pearls. While genuine pearls grow without human intervention in the wild in the molluscs and a nucleus is used for the production of cultured pearls, which is then coated with mother-of-pearl by the pearl animal, this nucleus is not used in the production of freshwater pearls. Instead, tissue parts of foreign mussels are inserted into other mussels via a small incision and then placed in fresh water. In this way, up to 50 pearls are formed per mussel, which are also given an optimal shape because they are not influenced by a nucleus. Freshwater pearls usually grow between two and six years before being harvested. In addition, freshwater pearls are easy to grow because they are not threatened by tidal waves or typhoons like seawater pearls. Today, most freshwater pearls are cultivated in China. A well-known variety among freshwater pearls is the Biwa pearl, which is cultivated in Lake Biwa in Japan. These pearls, which are often used in jewellery, have a smooth and beautiful shiny surface.