Assessing how different users of a Marine Protected Area perceive environmental changes can contribute to design management strategies. We assess how locals and tourists perceive environmental changes in the Cap de Creus protected area (NW Mediterranean, Spain). To identify locally perceived changes, we first conducted semistructured interviews with locals (n = 38). Reported environmental changes were then used to construct a survey applied to locals and tourists (n = 427). In semi-structured interviews, environmental changes were the least reported changes compared to economic and social changes and reports of negative environmental changes dominated over reports of positive environmental changes. Overall, all survey participants reported a decline of the health status of the local environment, with locals displaying higher levels of agreement with statements referring to coastal environmental deterioration than tourists. The predominance of responses reporting economic versus environmental changes can be explained by the recent radical transformation of the area towards tourism. Reports of coastal marine area deterioration are in line with available instrumental data. Higher levels of agreement with statements referring to environmental deterioration among locals than among tourists highlight the importance of people’s connection with nature to assess change. Considering that Cap de Creus has been protected for more than two decades, our findings raise concerns regarding its ongoing deterioration and underscore the importance of monitoring the effectiveness of marine protection to modulate management strategies.