Acid mine drainage (AMD), owing to its high content of potentially toxic elements (PTEs), impacts ecosystem health through the contamination of tributary rivers. This study evaluates the spatial and temporal distribution of arsenic (As), lead (Pb), and cadmium (Cd) in the surface waters and AMD of the Lake Uru Uru watershed, a Ramsar site within the Oruro mining district (Bolivia), and quantifies the associated pollution and ecological risk. A total of 27 surface-water samples were collected during the wet and dry seasons, and their concentrations along with basic water-quality parameters were examined. Results revealed that the three PTEs were highly elevated, with maximum concentrations of As 12.80 mg/L (wet season), Pb 37.80 mg/L at a site near the mine (dry season), and Cd 4.18 mg/L (dry season), all exceeding international safety thresholds. Principal component analysis (PCA) explained 70.3 % of the variance in the first two components (PC1 = 49.4 %, PC2 = 20.9 %), separating urban mining-impacted sites (CT-01, CR-01) from rural sites. The ecological risk index indicated 100 % of sites exhibited strong to extremely strong risk, with CT-01 and RH-02 (near the mine) most affected during the dry season.