Monitoring is a crucial component of conservation in marine protected areas (MPAs) as it allows managers to detect changes to biodiversity and to infer cause of change. However, the complexities of sampling designs and associated statistical analyses can impede implementation of monitoring by managers. Two monitoring frameworks commonly used in marine environments are statistical testing and parameter estimation. For many managers these two approaches fail to help them detect change and infer causation for one or more reasons: the complexity of the statistical test, no decision-making structure and a sampling design that is suboptimal. In collaboration with marine park rangers in Egypt, we instigated a monitoring framework to detect impacts by snorkelers in a pragmatic but scientifically rigorous way. First, we used a literature review to define causal criteria to facilitate inference. This was essential because our sampling design was suboptimal due to a lack of baseline data and there was only one impact site. Second, we established a threshold level of coral damage that if exceeded would trigger management to reduce the impact of snorkelers. This provided a clear decision-making structure. Third, we estimated effect sizes with confidence intervals to detect change. For the field managers, this approach to detection was easier to understand than assessing a null hypothesis and provided critical information for decision making. At no stage during the short study period did snorkelers cause damage that exceeded the threshold and thus mitigation was not required. In situations of technical and financial constraints this framework will increase the implementation of effective impact monitoring for many activities in MPAs and enhance management of marine biodiversity.