Adult fly collections were made in May and August 2006, from the mud of a salty lake in the Kiskunság National Park, Hungary. We collected 21,600 individuals of 62 species in May and 18,400 individuals of 81 species in August, giving a total of 103 species (only 40 appearing in both seasons). Dominant species were different in the two collections. Five species are new for the Hungarian fauna. Diversity measured by several indices was higher in the May collection. We observed simultaneously a nearly lognormal distribution and a power-law like behaviour of the abundances.