In the basin of the Ilmenau river in Nort Germany, groundwater abstraction has been increasingly used for field irrigation since the fifties. To determine the effects of this, baseflow is separated from time series of daily discharges 1956 to 1995 using the nonlinear reservoir model. Effective recharge and storage of groundwater is computed accordingly. Variation in precipitation has a higher impact on changes of these components over time than does the abstraction of groundwater. Relationships are determined by multiple regression. Groundwater abstraction causes a decrease of low flow, while the influence on regional groundwater storage is small.