Maximum water depth penetration and changes in horizontal distribution during 39yr of the emergent vegetation in Lake Krankesjon, S Sweden, were investigated. The capacity of the emergent vegetation to penetrate into deeper water areas was higher at wave exposed than at sheltered sites. Differences in biomass and biomass allocation of the dominant species, Phragmites australis, between an exposed and a sheltered site suggest that horizontal expansion towards deeper water at sheltered sites is limited by unfavourable substrate conditions.