A structurally dynamic model based on phosphorus nutrient limitation has been developed for Lake Mogan located nearby Ankara, Turkey. This eutrophication model, which includes very dense submerged plants, was calibrated using a standard procedure described by Jorgensen and Bendoriccho [Fundamentals of Ecological Modelling, 3rd ed. Elsevier, Amsterdam, 20 pp.]. Furthermore, exergy was applied as a goal function to consider the dynamic adaptation and the seasonality of plankton species (e.g. size shifts). This study provides the second case example by applying the exergy as a goal function in the calibration phase. The model was also validated using the data of another year. The results were consistent with the validations of the several lake models [Hydrobiologia 356 (1997a) 87; Hydrobiologia 379 (1998) 147; Hydrobiologia 445 (2001b) 1]. The model gives a fairly good performance in describing the competition between phytoplankton and submerged plants. (C) 2003 Elsevier Science B.V. All rights reserved.