Citizen Observatories (COs) are community-based environmental monitoring initiatives that invite the public to contribute observations, data and information in complement to authoritative, traditional insitu and remote sensing Earth Observation data. COs can play an important role in crucial areas such as climate change, sustainable development, air monitoring, flood and drought monitoring, land cover or land-use change. They can also provide new data sources for policy-making, and can result in increased citizen participation in environmental management and governance at a large scale. With the increasing prevalence of COs globally, there have been calls for a more integrated approach to handling their complexities, and to sharing knowledge for the design and management of stable, reliable and scalable CO programmes. Answering this challenge in the European context, the Horizon 2020-funded project WeObserve aims to improve coordination between existing COs and related European activities, while tackling three key challenges that inhibit the mainstreaming of citizen science, namely: Awareness, Acceptability, and Sustainability. This D2.4 Landscape Report frames the second part of a dynamic exercise to examine the three core challenges faced by these COs, and to consolidate the experience of a range of stakeholders into a set of recommendations for strengthening the ecosystem around COs in Europe.