Objective  Yongding River is an important water resource in Beijing. After a series of restoration measures in recent years, the ecological status of the river has recovered significantly. However, due to the unclear ecological background of the river, there are still some problems such as river discontinuity and substandard water quality, which affects its ecological service function. This study conducted an investigation on the status of water ecological quality to understand the ecological background and ecological service function of the river.

  Method  Based on the principle of zoning, classification and grading, the water ecological quality evaluation system was constructed by the analytic hierarchy process and principal component analysis method, with 14 indexes in the aspects of hydrology, habitat, water body, aquatic organism and social service, by combining subjective and objective methods.

  Result  The investigation results showed that the water quality index exceeded the standard in some areas and the nutrient content in sediment was generally high. The Yanchi-Sanjiadian section and Sanjiadian-Lugouqiao section had a long period of dry flow within a year, reaching 324 d and 309 d, respectively. The Shangqingshui-Zhaitang section was dry all year round. The evaluation results showed that all water sections of the river were in “relatively healthy” condition.

  Conclusion  The gorge section basically meets the requirements of ecological conservation functional area, and the plain section has certain social service function on the basis of maintaining its basic ecological function. The river ecological quality has obvious spatial distribution characteristics, and gradually deteriorates from upriver to downstream.