Global South cities have been characterised by the proliferation of informal settlements. Due to the speed and development of informal settlements being more ‘prone' to settle on environmentally sensitive areas, such as wetlands and setbacks of agricultural areas which ultimately have knock-on effects on water quality, estuaries, management of informal settlements, in dialogue with sustainability becomes critical when thinking about city futures. Informal settlements fundamentally challenge the core of urban planning. What happens when planners’ earmark environmentally sensitive (taboo) areas on their spatial plans, only to find that informal settlement communities are illegally occupying these areas? How is contemporary urban planning equipped to harness the necessary skill when dealing with the protection of the environment on one hand and assisting informal settlement residents on the other? Through exploring the management of Thembalethu Phase 1 of Upgrading of Informal Settlements Programme (UISP) in George, South Africa, the paper seeks to determine how built environment professionals involved in upgrading of the settlement challenged the role of professional planners and their ability to steer ‘informal’ occupation and development.