AbstractThe population structure, abundance (ind m−2), biomass and reproduction ofCorophium curvispinum, an important element of the littoral fauna, have been studied at four sampling stations on the northern shoreline of Lake Balaton (Keszthely Bay, Szigliget Bay, Bozsai Bay and Paloznak Bay) three times a year (spring, summer and autumn) inPhragmitesgrowing period from May 1991 to October 1993 and in summer 1994. The sampling stations represent the trophic gradient of the lake.The environmental parameters (Chlorophyll‐acontent of the plankton and of the reed periphyton, and suspended solid content of the water) were significantly higher (ANOVA) in the western basin (Keszthely and Szigliget bays) than in the eastern basin (Bozsai and Paloznak bays). However, the population parameters (length of the animals, percentage of juveniles, length of ovigerous females, percentage of ovigerous females and fecundity) did not differ significantly between the two basins. Both the abundance and biomass were higher in the middle than in the westernmost and easternmost bays but the difference is not significant.The ovigerous females were significantly bigger in spring than in summer and autumn. The egg number per female was also significantly greater in spring than in summer and autumn. The length of ovigerous females and the fecundity in summer did not differ significantly from those of autumn data.There is a significant positive correlation (Spearman rank correlation) between both abundance and biomass and the above environmental parameters. The length of ovigerous females and the fecundity were inversely correlated with the plankton Chlorophyll‐aconcentrations.The abundance ofC. curvispinumin the reed belt of Lake Balaton is greater than in several parts of the Dnieper and Volga. However, it is much lower than in the Don, Oka, Danube and Rhine r