The both polycentric governance and Living Labs concepts are based on decentralized participatory planning, co-design, and decisionmaking. While the concept of Living Lab is still emerging, the Isar-Plan (2000 ~ 2011) pioneered the approach for selecting, co-designing, and implementing nature-based solutions along the Isar River in Munich, Germany. Despite multiple governing authorities involved in the decisionmaking process of the Isar-Plan, the polycentric governance that led to the success of the project has to date not been analyzed. This paper presents the results of an ex-post-analysis of the Isar-Plan restoration planning process based on stakeholder interviews and a literature review. The contribution describes the evolution of Isar-Plan governance arrangements and discusses the Living Lab approaches to cooperative governance. The analysis demonstrates how polycentricity facilitated trust, learning, and the co-design of a resilient waterscape. The paper concludes that Living Labs can be a way of applying polycentric governance when autonomous and multi-scale decision-makers are collaboratively involved in the design of policy solutions, and vice-versa.