Acid mine drainage represents an extreme environment with high concentrations of potentially toxic elements and low pH values. These aquatic habitats are characterised by harsh conditions for biota, being dominated by acidophilic organisms. The study site, São Domingos mine, located in one of the largest metallogenetic provinces in the world, the Iberian Pyrite Belt, was closed without preventive measures. To identify the algae species and understand the relationships with abiotic parameters of the ecosystem, water and biological material were collected and analysed. Digital terrain models were obtained with an unmanned aerial vehicle for geomorphological and hydrologic characterisation of the mine degraded landscape. The results show two types of algal colours that seem to represent different degrees of photosynthetic activity. Optical and scanning electron microscopy revealed 14 taxa at the genus level, divided into eight classes. The genus Mougeotia is the most abundant multicellular algae. With respect to unicellular algae, diatoms are ubiquitous and abundant. Abiotic analyses expose typical features of acid mine drainage and support an inverse relationship between chemical contamination and biological diversity. Factorial correspondence analysis indicates three groups of attributes and samples by their relationship with specific toxic elements. This analysis also suggests a close association between Spirogyra and Pb, together composing a structurally simple ecosystem. The highest contamination in the river system is related to the hydrologic patterns obtained from photogrammetric products, such as the digital surface model and flow map accumulation, indicating the input of leachates from the section having the finest sulfide-rich wastes. Information about the algae community and their association with flow patterns of toxic elements is a relevant tool from a biomonitoring perspective.

Abandoned mines pose environmental risks due to the accumulation of sulfide-rich waste, which generates acid mine drainage and produces fine-grained, unconsolidated materials that, when deposited on steep slopes, accelerate erosion and contaminant transport. This study assesses the environmental impact of the Trimpancho mining complex by integrating UAV-based photogrammetry, water analysis, and mine waste characterization. Aerial surveys produced high-resolution orthomosaics and digital surface models, enabling the identification of runoff patterns, erosion hotspots, and waste accumulation. The estimated waste volume is approximately 253,377 m³ . Key findings highlight critical erosion areas on steep slopes (>30°) where waste mobilization enhances metal and sulfate transport into the Trimpancho stream, affecting the Chança River. Water samples have pH values ranging from 2.59 to 8.27, electrical conductivity peaking at 4171 µS/cm, and elevated concentrations of iron (65.7 mg/L), aluminum (174 mg/L), manganese (23.5 mg/L), and zinc (20.7 mg/L). Mine waste characterization revealed that Nuestra Señora del Carmen dump exhibited higher leaching potential compared to Volta Falsa. This study underscores the value of UAV technology for cost-effective and high-resolution environmental monitoring in abandoned mines. The results emphasize the need for targeted remediation strategies and water quality improvement. This multi method approach can serve as a model for assessing contamination risks and optimizing environmental monitoring programs in other legacy mining sites.