Freshwater fish diversity of the Yongding River, the largest river flowing through Beijing.

Background: The Yongding River, the largest river flowing through Beijing, is a major tributary of the Haihe River system. It holds significant ecological, economic and social importance in northern China. However, due to the climate change and anthropogenic activities, parts of the tributaries and lower mainstream of the Yongding River have dried up in recent decades. To alleviate the water scarcity crisis of the Yongding River, ecological water replenishment was initiated in 2020 based on the Middle Route of the South-to-North Water Diversion Project and the Wanjiazhai Yellow River Diversion Project. As a result, the fish population structure and diversity of the Yongding River may change accordingly. In this context, before large-scale water replenishment started, we conducted two field surveys in the summer and autumn of 2019 to assess fish diversity in the Yongding River Basin. New information: This study provides information of 45 fish species belonging to nine orders, 18 families, seven subfamilies and 33 genera in the Yongding River Basin. Our study includes one dataset that presents taxonomy, distribution, water body and location for each species collected from the Yongding River. The provided data can assist other researchers in assessing the impact of water replenishment on aquatic biodiversity and the broader ecological environment of northern China.