The monogenean fauna on crucian carp, Carassius carassius L., collected from Golbasi Dam Lake during the period from May 2003 to April 2004, were studied to assess the effect of water temperature on parasite prevalence and abundance. A total of 132 fish were studied over a 12-month period. These revealed two species of monogenean Dactylogyrus anchoratus and Gyrodactylus carassii. In terms of seasonal occurrence, Gyrodactylus carassii represented the dominant parasite species being recorded on host gills throughout the year. The total prevalence of infection of G. carassii was 66.7% with the infection rates varying from a peak of 100% in May and June 2003 to a low of 20% in December 2003. Abundance of this species also showed a peak in May-June, followed by a sharp decrease thereafter and a subsequent rise in the following April. Water temperature was an important variable and a significant positive correlation was found between parasite abundance and water temperature. (K-W H=91.001, p < 0.0001). Dactylogyrus anchoratus was recorded in 48 out of 132 fish that were examined (36%). The prevalence levels of this species were somewhat erratic and D. anchoratus infection varied according to the season and reached its highest values in May (100%). The prevalence and abundance of D. anchoratus appeared to be correlated with the water temperature even when it was optimum for D. anchoratus (K-W H=72.917, p < 0.0001). Consequently, the parasite prevalence and abundance appears to be influenced by water temperature.