To solve regional environmental problems, there is a trend of establishing urban agglomerations and formulating cooperative policy institutions in China. The extant studies on policy institutions largely focus on the coordinative mechanisms of multiple actors within one single institution. Only a few studies have tried to understand how different policy institutions are interlinked and mutually affected to influence actors’ decisions and problem resolutions. This article applies a network-based analytical approach and adopts the Ecology of Games Framework to explore how regional environmental governance is coordinated in the Guangdong-Hong Kong-Macao Greater Bay Area. It was found that coordinative mechanisms in regional environmental governance can happen around three elements: policy institutions, policy actors, and policy issues. Policy institutions tend to serve as an umbrella for many diverse and interdependent activities and actors within individual institutions. Additionally, positive externalities emerging between different policy institutions perform as coordinators across institutions. For actors, state-level actors usually play as facilitators of policy institutions while they are not active in participating in policy games in later phases; it is regional actors, particularly from Guangdong, that are active in the operation of policy institutions. For policy issues, they emerge because they are often tied with each other, and some of them play as the common ground for seemly separating policy institutions.