Abstract

The Tigris River, extending about 1,900 km from Syria into Iraq — with roughly 1,415 km passing through Iraqi territory and a drainage basin of 235,000 km² — provides a crucial resource for both drinking and household needs. However, rapid urban growth and the discharge of untreated wastewater have severely impacted its quality. The Weighted Arithmetic Water Quality Index (WAWQI) was employed in this article to assess seasonal variations in the quality of water of the Tigris River in Baghdad City. During 2022, water speceimens were collected from three key treatment facilities: Al-Kadhimya, Al-Karama, and Al-Wathba. Ten physicochemical parameters were measured: pH, turbidity, calcium (Ca²⁺), total hardness, fluoride (F⁻), electrical conductivity (EC), magnesium (Mg²⁺), water temperature, alkalinity, and total dissolved solids (TDS). Results revealed clear seasonal patterns: most parameters reached their highest levels in winter, while pH and temperature were elevated in summer; turbidity and alkalinity peaked during spring. The Water Quality Index (WQI) calculations placed the Tigris River mainly within the E-grade category (unsuitable for drinking and aquatic life) across all seasons. A slight quality improvement was observed in autumn at Al-Kadhimya (WQI = 104.26) and Al-Karama (WQI = 105.20), where water quality shifted from unsuitable to poor (C-grade). Downstream, overall water quality continued to decline. The study links this deterioration primarily to unregulated wastewater discharge, erosion of riverbanks, and surface runoff from nearby areas. The results underscore an urgent call to strengthen wastewater management and enforce stricter environmental controls, and regular water monitoring to safeguard the Tigris River’s ecological and public health functions.