The aim of this study was to characterize the mud crab Rhithropanopeus harrisii ssp. tridentatus that occurs in the Dead Vistula. Of the 220 specimens collected, 57% were males and 43% were females. Females with eggs on the pleopods were present throughout June, July and August. The carapace width varied from 4.9 mm to 22.4 mm and length ranged from 4.1 mm to 16.3 mm. The highest frequency (49.1%) was observed in the 9.1-13.5 mm width class. The wet weight of the specimens varied from 0.045 to 4.299 g. The results obtained indicate that no significant changes in the morphology or life cycle of the R. harrisii tridentatus from the Dead Vistula River have occurred in the last 30 years.