<p>Groundwater sustainability policies can help reduce and mitigate the effects of groundwater depletion. While such policies are important, how they are implemented is a critical determinant of their success. During implementation, agencies must decipher the policy and translate it into actions. If there are multiple ways to interpret the policy (i.e., when there are ambiguities), implementing agencies must make subjective decisions regarding implementation. As a result, groundwater sustainability policies may fail to achieve their intended goals. A key step for facilitating the implementation of such policies is to identify when and why ambiguity is likely to arise. This research examines ambiguities during implementation of California’s Sustainable Groundwater Management Act. Six factors (agency discretion, credibility gaps, policy gaps, policy overlap, information gaps, and knowledge gaps) contributed to four ambiguities (means, goal, oversight, and authority). These ambiguities contributed to variation in implementation and increased the amount of effort required of agencies to interpret the policy and translate it into action. Policymakers and practitioners can learn from California’s experience and take steps to design and implement groundwater sustainability policies in ways that reduce variability and help ensure groundwater sustainability goals are achieved.</p>