Water governance worldwide is going through a shift towards more holistic and participatory approaches. In Europe, the EU Water Framework Directive (WFD) adopted in 2000, aims at protecting surface water and groundwater. The WFD emphasizes the importance of stakeholder participation in planning and implementation of the directive, and in order to reach environmental objectives. However, the empirical findings are insufficient regarding how stakeholder participation can lead to improved decisions and implemented plans. In Sweden, a major water quality problem is eutrophication caused to a large extend by diffuse nutrient leakage from agriculture. Therefore, it is important to involve farmers in water management, since their participation can lead the commitment of mitigation measures for reduced nutrient leakage. The overall aim of this study is to contribute the knowledge and understanding of active stakeholder participation in water management, in particular how it can lead to implementation of water quality objectives. The thesis addresses stakeholder participation in eutrophication management in local Swedish catchments, with a particular focus on farmers’ participation in the commitment of mitigation measures. The results are based on case study research, involving four catchment areas in Sweden with severe eutrophication problems. The thesis identified socio-demographic factors, farmers’ knowledge, and the level of existing information and economic support for wetland creation, as factors affecting farmers’ willingness to participate in wetland creation to mitigate nutrient leakage. In the local catchment groups studied, farmers and other local stakeholders participated to discuss potential mitigation activities. In these, farmers emphasized other emitting actors’ responsibility and commitment in local action plans. Where this was realized, social capital within the group increased and led to further collaboration. The thesis also analyzed large-scale wetland programmes at catchment scale, where the organizational and institutional arrangements were central to realize farmers’ participation: inter-municipal agreements entailed sufficient resources, the organization involved the most relevant actors; and leadership resources were important. The thesis argues that organizing water management at a catchment level can be important to cope with challenges related to stake-holder participation for mitigating diffuse nutrient leakage. In particular for dissemination and collection of information, suggesting potential measures for all concerned actors, provide resources needed to realize actions, and to build trust and collaboration. The thesis also emphasized that stakeholder participation has to be underpinned by a genuine meaning, both for the initiators and the participants.