Not impossible... folks 'round there had 'better' things to do lately then document the history of local gems. 'Bet no book mentions Moldavian pearls either, yet local tradition mentions some production of seed pearls used for embroidery, buttons - never an 'industry' just occasional wild harvest. I have only heard the folklore: stories about pearl embroidered items donated to churches in the region roughly between 1650-1780. I doubt any documentation exists and I have not tried to locate any - the legend sounds rather nice (a pity to waste that first impression!).

If anything, the pearls must be truly old. Hard to believe that any production of local pearls may have continued into the 1900s even.

After all, to have local pearls all you need is a population of humans harvesting a population of freshwater mollusks for a few generations, and a handful of willing buyers capable to amass the occasional pearls. The conditions apply to Croatia as well as East Germany (where natural river pearls are documented).

Just a thought...

The pearls in the picture could be anything, but the claim is not quite science fiction in my opinion.