Study on the Health Assessment of Rivers and Lakes on the Qinghai Plateau Based on an AHP–TOPSIS Model

Under global environmental change, the health of rivers and lakes on the “Asian Water Tower”—the Qinghai–Tibetan Plateau—is facing mounting pressures. This study examines Qinghai Lake, the Huangshui River, the Golmud River, and the Qinghai reach of the Yangtze River. By integrating the Water Quality Index (WQI) with the AHP–TOPSIS framework, we develop a multidimensional assessment system encompassing water resources, water environment, aquatic ecology, and management functions. The WQI results reveal pronounced spatial heterogeneity in water quality, with conditions ranked as Golmud River > Yangtze River > Huangshui River > Qinghai Lake. Dominant controlling factors also shift from dissolved oxygen in riverine systems to total phosphorus in the lake environment. The comprehensive AHP–TOPSIS evaluation further shows a health ranking of Yangtze River (0.736) > Golmud River (0.602) > Qinghai Lake (0.404) > Huangshui River (0.297), leading to the identification of four distinct management pathways: ecological conservation, natural restoration, nutrient control, and pollution remediation. By moving beyond single-parameter diagnostics, this study provides a robust methodological basis for differentiated river–lake management. The proposed “one river (lake), one strategy” framework, coupled with red-line management recommendations grounded in key indicators, offers direct scientific support for systematic protection and precise governance of aquatic ecosystems on the Qinghai–Tibetan Plateau, contributing to national ecological security and high-level environmental stewardship.