Abstract: Total phosphorus(TP) in the Changjiang River Basin is the primary standard-exceeding pollutant that has attracted much attention, and it has a significant influence on the aquatic ecology.The concentrations and changing trends of TP in the Changjiang River Basin′s main stream, key tributaries, lakes, and reservoirs are studied from 1998 to 2023.The results show that: ① The TP concentration in the main stream of the Changjiang River shows an overall increasing trend from the source of the Jinsha River to the Yangtze River Estuary, but TP concentrations in all reaches are below the Class Ⅲ standard limit of 0.20 mg/L.In the section of the Changjiang River main stream from Yibin to the Three Gorges Dam, the TP concentration is generally higher during the wet season than during the dry season.In contrast, the concentration in the Yangtze River Estuary area is higher during the dry season than during the wet season.② Over the past two decades, the phosphorus speciation in the main stream of the Changjiang River, particularly in the stretch from Yibin to the outlet of Dongting Lake, has undergone significant changes.This shift has primarily been driven by a substantial reduction in sediment load in the main stem, resulting from the operation of the Three Gorges Reservoir and the cascade reservoirs in the lower Jinsha River, as well as soil and water processes across the basin.The current speciation characteristics are as follows: in the section from Yibin to Qingxichang, phosphorus is predominantly in particulate form during the wet season, while dissolved forms dominate during normal and dry seasons.From Qingxichang to the outlet of Dongting Lake, dissolved phosphorus is the main form across all hydrological periods.In the stretch from Wuhan to Xuliujing, particulate phosphorus is slightly higher than dissolved phosphorus.In the Yangtze River Estuary, particulate phosphorus remains the dominant form throughout all hydrological periods.③ Over the past decade, the TP concentration in the main stream of the Changjiang River and most of its major tributaries has shown a systematic decline, primarily driven by water pollution control and the management of "three phosphorus" sources.Compared to peak concentration years, the concentrations of CP (clarified sample total phosphorus), TP (original sample total phosphorus), and DP (dissolved phosphorus) in the main stream of the Changjiang River have all decreased by more than 50% during 2021~2023.The reduction rates of CP concentration in some major tributaries are as follows: Minjiang River 68.9%, Tuojiang River 59.2%, Jialing River 66.7%, and Wujiang River 92.6%.④ In the Changjiang River Basin, 84% of the lakes have TP levels exceeding the Class Ⅲ water quality standard limit either year-round or seasonally.Elevated TP remains one of the key ecological and environmental issues for most lakes in the basin.In contrast, the incidence of TP exceeding standards in reservoirs across the basin is significantly lower than that in lakes.