Caldesia parnassifolia is a critically endangered and strictly protected species in Hungary. It was known only from one locality of occurrence so far, where it was last reported in 2003. Its new occurrence was discovered in Somogy county, in 2010. It appeared in an artificial pond created in the place of an originally swampy depression. Based on this newly discovered occurrence we can assume that other potential populations might still exist in South-Transdanubium, which could be rediscovered if similar conservation measures occur.