[en] This paper describes an object-oriented approach to river basin simulation modeling that is event driven rather than time driven as are most river system simulation models. At the heart of this method are autonomous software objects which replicate the physical behavior of the components of an actual river system (Colorado River). These objects react to stimuli (changing values of their inputs, outputs or state) in much the same way as do the analogous components of the actual river. The simulation of river systems is the result of the coordinated actions, in any order, of the various objects representing the entities within the system. An object-oriented approach to modeling a river has a number of characteristics that make it worthy of consideration. The model's architecture makes it especially suited to graphic user interfaces and database operations. It allows the easy integration of artificial intelligence techniques that can aid in expressing complex policies governing system operation