Coordination mandates are used to steer collective action between local government agencies. When higher levels of government allow agencies to choose how to work together, the organizational forms and institutional arrangements they adopt likely influences their ability to achieve mandated coordinated outcomes. How group-level interactions influence achievement of coordinated outcomes is not well understood. California’s Sustainable Groundwater Management Act (SGMA) provides opportunity to shed light on this topic. SGMA is a state-legislative mandate that requires local agencies who share groundwater basins to undertake groundwater sustainability planning. The mandate affords agencies leeway in deciding how they engage with one another so long as they meet multiple requirements for coordinated outcomes. Drawing on institutional theories of collective action and ethnographic data collected from 2018-2022, we employ multi-value Qualitative Comparative Analysis (mvQCA) to examine how configurations of organizational forms and institutional arrangements adopted by agencies in 18 groundwater basins influenced their achievement of coordinated outcomes. Our findings highlight the importance of adopting collaborative institutional arrangements. Yet, the specific configuration of collaborative institutional arrangements varies depending on the type of coordinated outcomes agencies are mandated to achieve. These findings point to the need for mandates to require adoption of collaborative institutional arrangements, the specific configurations of which will be dictated by the requirements of the mandate.