The practice of landscape architectural involves forming the space in our cities and suburbs, as well as the landscape surrounding. The need of exploiting green environment leads up to, among other issues, flood problem during heavy rain and overfed water environments. The problem is partially caused by the shortage of knowledge, how the environment is responding of the innovations made by the city- urban planning and how to get sustainability. Research and knowledge how to take care of our environment, in a natural way, is increasing. The object of the thesis is to propose control and balance in urban wetlands, and discuss the difference a plant design can do. The thesis deals with discourses in the field of landscape architecture, biological diversity, dam construction, limnology, planting design and management, pollution of the environment and urban design practice. The thesis implicates case studies, literature studies, botany, and management all regarding wetlands. These studies attempt to understand the plant and management complexity in a wetland environment. The thesis is comprehending argumentations how to create a biological multiplicity with plants, within the different zones a dam structure embrace. The theoretical basis for argumentation, and the methodological tools applied in the task "Vallentuna våtmark" are a result of my disquisitions.