As already mentioned in Chapter 18, models are powerful management tools that can synthesize and integrate our knowledge about the environmental problems of ecosystems. It should be emphasized that models not only integrate the knowledge based on observations (data) but also are able to include in the synthesis our scientific knowledge, knowledge about allometric principles, knowledge about food items and food chains, and so on. Models can be applied to answer relevant environmental management problems—how will the ecosystem be changed if these and these forcing functions (ecosystem impacts) are changed? It is therefore clear that aquatic ecosystem management without models would be almost impossible. Models are an indispensable tool in environmental management in general.