Ecotourism activities alter diversity of bacteria, archaea, and fungi in the freshwater stream of the Agua Azul Waterfalls in southeastern Mexico

Natural freshwater streams harbor diverse microbial communities that support ecosystem functioning. Due to their great biodiversity and geomorphological characteristics, these ecosystems are often very attractive ecotourism destinations, which makes them highly vulnerable to anthropogenic disturbances. The Agua Azul Waterfalls (Cascadas de Agua Azul, in Spanish), a major tourist destination located in indigenous territories of southeastern Mexico (Chiapas, Mexico), offer a unique setting to investigate how sustained human activity influences microbial diversity and quality of water and sediments. To determine the ecological sensitivity of this freshwater stream to tourism pressure, we sampled sites spanning gradients of tourist activity and conducted an integrated analysis of water and sediment physicochemistry, elemental composition, and the composition of microbial communities (bacteria, archaea, and fungi). Areas associated with ecotourism activities showed notable changes in physicochemical parameters and microbial community composition, indicating localized impacts on this ecosystem. Furthermore, evidence of effective management by local Indigenous communities suggests a partial mitigation of anthropogenic disturbances through ecotourism activities. Our findings highlight the potential of microbial diversity in combination with physicochemical parameters as a tool to detect early stages of human impacts on freshwater ecosystems and establish a basis for future monitoring and conservation efforts. The distinctive characteristics of this site position it as a promising model for advancing our understanding of microbial diversity and the dynamics of freshwater stream ecosystems. ImportanceThis study shows evidence that ecotourism is already impacting the biodiversity and water quality of Agua Azul Waterfalls, a freshwater stream located within a protected natural area in southeastern Mexico. While the water still meets basic quality standards, areas with higher tourist activity show early signs of nutrient enrichment and measurable changes in the types of microbes present and the roles they play in this ecosystem. As the first analysis of microbial diversity in this ecosystem, our work highlights the value of microbes as early and sensitive indicators of human impact. By directly comparing tourist and non-tourist areas, we provide evidence of how recreational pressure is transforming this freshwater environment. We expect that our findings will help guide local communities and policymakers in creating more sustainable tourism practices to preserve the cultural and economic value of this ecosystem before irreversible damage occurs.