Abstract
The main pollutants in the Koshkar-Ata water system include heavy metals (zinc, lead, copper, and cadmium), sulfates, nitrates, and petroleum hydrocarbons. Many of these substances originate from the tailings and slag accumulated during the operation of the former Shymkent Lead Plant and other metallurgical facilities. Field and laboratory studies have shown that the concentrations of several heavy metals in river sediments and groundwater exceed the maximum permissible concentrations (MPC) by tens or even hundreds of times. These toxic elements exhibit high persistence, low solubility, and strong accumulation tendencies, which result in long-term ecological degradation. The conducted assessment demonstrates that the Koshkar-Ata River in Shymkent is one of the most severely polluted urban water bodies in southern Kazakhstan. The river’s hydrochemical composition clearly reflects the influence of long-term industrial activity, particularly from historical metallurgical production and uncontrolled wastewater discharge. Concentrations of heavy metals such as copper, zinc, and lead, along with high levels of organic and nutrient pollutants, significantly exceed established environmental standards and threaten the ecological stability of the entire basin.The findings confirm that the Koshkar-Ata River has lost its natural self-purification capacity and requires immediate rehabilitation measures.