This paper aims to analyse the nexus between tourism activities, including tourists’ circulation, accommodation or entertainment, and environmental degradation. Consequently, the conceptual framework captures the complexity of the nexus between tourism and the environment, given that tourism activities can be performed by tourists or for tourists and that tourism depends on the environmental quality, and, consequently, we highlight the impact of tourism activities on biodiversity loss through the pollution effects that they generate, i.e., air pollution, water pollution, or noise pollution, as well as their contribution to waste increase or to the depletion of natural resources. To achieve this goal, we apply structural equation modelling based on partial least squares analysis (PLS). The results based on tourists’ opinions highlight the existence of a direct and significant nexus between tourists’ activities and environmental degradation, with many implications and consequences.