DISCLAIMER: The present Project Deliverable has been submitted to the European Commission for review. The information and views set out in this report are those of the author(s) and do not necessarily reflect the official opinion of the European Union. Neither the European Union institutions and bodies nor any person acting on their behalf may be held responsible for the use which may be made of the information contained therein. ______ CoAct (Co-designing Citizen Social Science for Collective Action) aims at co-designing concepts, methods and tools for Citizen Social Science around wicked global social issues. Four different research and innovation (R&I) actions organised the empirical work of CoAct and this report presents the process of building the knowledge coalition network for one of those R&I actions developed in the frame of CoAct WP5. This R&I action aims at co-designing citizen social science tools to facilitate actions contributing towards Environmental Justice in the Matanza-Riachuelo river basin. The basin covers 64 km-long and 6 million people live there, most of them in vulnerable socio-environmental situations. In particular, we aim at co-designing a digital platform to produce and share data that can contribute to mapping different socio-environmental problems as understood by a diversity of stakeholders and promote concrete actions for addressing those problems. The Knowledge Coalition works as a network of actors that intervene throughout the project’s R&I cycle, by discussing, defining, and co-designing different activities. We define it as the network of stakeholders who are interested in and informed about the R&I project goal and vision and who play an active role, either participating in or co-designing different actions. We expect the network to be continuously evolving and different types of commitment by a variety of actors is foreseen over time, depending on expertise, interests, synergies and project activities. FARN and CENIT/UNSAM identified three different types of actors that would be part of the Knowledge Coalition: researchers working in academic organisations doing research about different socio-environmental problems of the basin; public policy actors from the different jurisdictions involved in the basin (Municipal, Provincial and National) and community actors, which includes people living or working who belong to territorial organisations and also civil society organisations (CSOs) at large. We had to modify our original plan for the Knowledge Coalition creation due to the Covid-19 pandemic and associated lockdown restrictions. We organised three types of virtual engagement activities with candidates to be part of the Knowledge Coalition: interviews, micro-workshops and a platform co-design workshop. In total we reached around 30 actors (research groups, public policy organisations and territorial and civil society organisations) inside and outside the basin, who participated in some of those instances and expressed their interest in being involved in the R&I action’s future activities. We managed to identify main socio-environmental problems in different locations in the basin as understood by different stakeholders who participated in our action. We also started to delineate the main purpose of the citizen driven platform, which will initially systematise and co-produce information on three main socio-environmental themes: conservation of green areas, water quality and relocation of people living in areas with environmental risks.