Protected areas (PAs) represent a powerful refuge for maintaining and safeguarding biodiversity. Generally, PAs are delineated to protect terrestrial taxa, providing incidental protection to the aquatic ecosystems within their borders. Here, we compare water quality within PAs and non-PAs in southern Brazil, encompassing remnants of the Atlantic Forest biome, to assess whether PAs serve as a buffer from external pressures for aquatic ecosystems within their boundaries. In addition to physicochemical and microbiological water parameters, we analysed 147 pesticide and 31 pharmaceutical compounds in water samples from 33 sites within and outside PAs. The water quality did not differ between PAs and non-PAs but indicated clear pollution from sewage discharges. We found 19 pesticides and five pharmaceuticals in streams within the study area. We detected pesticides in all sampling sites, with the herbicide 2,4-dichlorophenoxyacetic acid present in 91% of them. Our data show that PAs are insufficient means to mitigate the impacts stemming from their catchments, and the running water that reaches their domains already shows signs of anthropogenic interference, which may affect aquatic biodiversity. Protection and management measures require consideration of the whole watershed to protect freshwater habitats and biota.

保护区 (PA) 是维护和保护生物多样性的强大避难所。通常，划定保护区以保护陆地分类群，为其境内的水生生态系统提供附带保护。在这里，我们比较了巴西南部保护区和非保护区内的水质，包括大西洋森林生物群落的残余物，以评估保护区是否可以作为其边界内水生生态系统外部压力的缓冲。除了物理化学和微生物水参数外，我们还分析了保护区内外 33 个地点的水样中的 147 种农药和 31 种药物化合物。保护区和非保护区之间的水质没有差异，但表明污水排放造成明显污染。我们在研究区域内的溪流中发现了 19 种农药和 5 种药物。我们在所有采样点检测到农药，其中 91% 存在除草剂 2,4-二氯苯氧乙酸。我们的数据表明，保护区不足以减轻其集水区产生的影响，并且到达其领域的自来水已经显示出人为干扰的迹象，这可能会影响水生生物多样性。保护和管理措施需要考虑整个流域，以保护淡水栖息地和生物群。