Large-scale coal mining and production activities generate mine wastewater, which can damage the aquatic ecosystem of rivers. This study focuses on a section of a small watershed in the southwestern coal mining area of Guizhou Province. Eight heavy metals in water were analyzed for their distribution and pollution characteristics. The irrigation suitability and water pollution degree were evaluated using multiple indicators including water quality index, heavy metal pollution index, and sodium adsorption ratio. A Positive Matrix Factorization (PMF) model was ultimately employed for heavy metal source tracing in collected water samples. The results show that the concentration of Fe and Mn in surface water had the highest exceedance rates, reaching 100%, with most occurrences concentrated in cross-sections near mining areas. Maximum heavy metal concentrations were recorded in August (summer), while minimum values were observed in December (winter). Significant ecological risks were identified through multi-indicator evaluation, particularly regarding irrigation applications and aquatic environments. PMF analysis revealed that Fe and Mn pollution was primarily attributed to mining operations, mineral processing activities, and open-pit tailings. Sb contamination was determined to originate from geological sources, whereas As pollution was mainly linked to anthropogenic activities including agricultural practices and rural drainage. These findings were considered valuable for establishing protective measures, conducting ecological assessments, and implementing pollution control strategies in surface water ecosystems of mining areas.