The central role of macrophytes for the functioning of aquatic systems means that the most effective way to manage these systems is often through vegetation management. For this we need to understand the mechanisms regulating vegetation distribution. Submerged macrophyte distribution is mainly related to water depth, water transparency and epiphytic growth. The distribution of emergent vegetation can largely be predicted from water depth and substrate characteristics. Also, in both submerged and emergent macrophytes, the effects on the vegetation of grazing can be dramatic. Management should aim at providing environmental conditions favouring the desired ecosystem state, rather than methods directly aimed at the vegetation. For example, the best method for promoting establishment of emergent vegetation is often lowering of the water level. To establish submerged vegetation, water transparency can be increased through biomanipulation (the removal of zooplanktivorous fish leading to increased zooplankton grazing pressure on phytoplankton). Changes in water depth and introduction of grazers are often effective measures to control growth of aquatic weeds.