Planners of development interventions often assume that natural resource use and management problems can be addressed by applying a single model for different village communities. This perspective fails to recognize the fact that villagers are not passive recipients of interventions, but that they are actively engaged in the shaping and adaptation of external law, rules, and regulations to fit locality-specific situations. Also, most institutional studies have a sectoral approach focusing on one type of natural resources only and failing to consider the mutual dependency of different resources and their users in multiple resource systems. In order to address these issues and develop a better understanding of local dynamics and differences through time and place, we need a study that recognizes the multiple resource systems and the critical role of human agency in solving resource use problems. This PhD research focuses on the use and management of water and forest as integrated resource systems to assess the process of institutional bricolage as a result of external interventions and modernization. The study includes six cases of micro spring forests on Ukerewe main Island in Lake Victoria, Tanzania, and describes the role of resource users in negotiating, transforming and adapting the newly introduced institutions to the locally existing institutional frames. Villagers usually see the management of water sources as interrelated with the management of the micro spring forest vegetation. The study demonstrates to what extend and how changes in the institutional organisation for the use and management of water sources affect the forest vegetation. Modern resource governance is usually carried out along sector lines. Results from these cases clearly underscore the need to regard water sources and forest vegetation as integrated resource systems, and to organise structural interventions accordingly, which is along inter-sector or inter-departmental lines of intervention.