In this study, helminth parasites in tench of Kovada Lake and seasonal variation of these parasites were investigated monthly from March 2003 to February 2004. A total of 6 species of helminth parasites were found on 51 of 105 fish examined. The following parasites were found: Gyrodactylus medius, Asymphylodora tincae, Caryophyllaeus laticeps, plerocercoids of Ligula intestinalis, Proteocephalus torulosus and Bothriocephalus acheilognathi. Asymphylodora tincae was the most common parasite species found in tench with infected fish collected in all months sampled. Infection levels peaked in December (42.8%). Infection levels of the second most commonly found parasite C. laticeps, peaked in April (42.8%). Ligula intestinalis, the third most common parasite was more prevalent in October (20%). The fourth most common parasite P. torulosus was found only in June (27.2%). The fifth most common parasite G. medius was found only in January. The remaining parasite, B. acheilognathi was only present in small numbers with a total of 5 individuals being collected from the intestine. Proteocephalus torulosus is a new record for freshwater fishes in Turkey. Caryophyllaeus laticeps was recorded for the first time in tench in Turkey.