Including members of the public in the development of effective environmental monitoring systems is gaining traction. This research assesses the potential for a hybrid monitoring system for the case of coral at the Great Barrier Reef. Based on a review of citizen-derived data sources, the paper first develops a framework and then populates it with five datasets. These are then compared based on data volumes, type of data, spatial coverage, and bleaching patterns. The results reveal the inherent difficulties – both in terms of quantity and quality – for collective sensing data (Twitter in this case) and more structured human sensors approaches (Eye on the Reef Sightings). However, more targeted approaches, such as CoralWatch and tourism-operator based data collection, emerged as important contributors to information generation on the state of coral. Citizen-based data that either deliver a high data density per location, a wide geographic coverage, or regular observations over time are particularly valuable. Recommendations are made for developing a hybrid monitoring system that integrates citizen-derived with professionally collected data.