This article focuses on self-organizing processes in contested urban social-ecological systems. It analyzes a wetland conservation program and civic management effort in the Angachilla sector of the city of Valdivia, Chile in a 15-year time frame. The aim is to understand what triggers collective actions and self-organization in the attempts of preserving an urban green common. The study uses a qualitative approach based on action-research methodologies. It examines key variables influencing self-organizing processes; including social-environmental crises, governance vacuums, wetland valuation, and leadership. It also discusses collective strategies for the transformation of negative feedback loops, such as norms and regulations detrimental to wetland protection, and those related to resistance to change of wetland surface area due to unregulated urbanization. From an Urban Green Commons perspective, this work illustrates the complexity of dealing with contested nature, making it a resource difficult to govern collectively given all the different interests and values in place. It also shows that there have been successful periods of active wetland management that have influenced active democratic processes regarding land use and land use change in the city.