In this article, we go back on two ways of taking into account the environmental dimension in urban planning and governance. We stress the difficult articulation between these two approaches – “urban ecology” and “urban environment” – and the actual impasse the discipline of urban planning finds itself in in its quest of the sustainable city. These two approaches for acting on the city by considering the complexity of its milieu build on different representations of this milieu and different modes of action legitimation. Negating each other, they can difficultly coexist, even less articulate. Through the example of water management in Cochabamba, we stress the tensions between these approaches. We point also to the awkward and marginalized position of urban planning and challenges it must face to regain a capacity of action in contemporary fragmented cities that know complex governance landscapes and rare or endangered resources