ABSTRACT
The wide use of ecological models in environmental management started around 1970, when the first eutrophication models emerged and very complex river models were developed. These models may be named the third generation of models. They are characterized by often being too complex, because it was so easy to write programs for a computer, which was able to handle rather complex models. The modeler would then anyhow study the relevant references before his or her final model is developed in order to build upon previous modeling experience. Provided that the general modeling recommendations are followed and the underlying database was of good quality, it was possible to develop models that can be used as prognosis tool. The shortcomings of modeling were, however, revealed in this period, too. It became clear that the models were rigid in comparison with the enormous flexibility that was characteristic for ecosystems.
