【Objectives】 The mainstream of the middle and lower Hanjiang River serves as a vital drinking water source for cities along its banks. During the summer of 2025, the middle and lower reaches of the Hanjiang River were suffered from the dual stress of extreme low water and high tempertures, coupled with cyanobacterial blooms broke out in the mainstream, which severely threatening the drinking water supply safety of water sources for cities along the river. This study is designed to investigate the mechanisms by which cyanobacterial blooms are affected under extreme hydro-meteorological conditions and their impacts on water supply from drinking water source areas.【Methods】 In the summer of 2025, specifically from August 25 to 29, the project team conducted monitoring of water quality and aquatic ecological indicators at drinking water sources in the main stream of the middle and lower reaches of the Han River. It also carried out a dedicated survey of water supply plants in major cities, focusing on assessing water treatment processes, the capacity to treat algae and taste-and-odor compounds, the extent of cyanobacterial bloom impacts, and relevant response measures.【Results】The results indicate that a large-scale cyanobacterial bloom occurred in the main stream of the middle and lower reaches of the Han River. It was mainly distributed in the river section from Yicheng City to the Zongguan Water Plant in Wuhan, with mild blooms predominating. Moderate cyanobacterial blooms were observed in water source areas including those in Zhongxiang, Xiantao, and Chengnan in Hanchuan, among other sites. The total algal density ranged from 2.12 × 10⁷ to 7.10 × 10⁷ cells/L. The dominant species all belonged to the cyanobacterial genus Pseudanabaena. Cyanotoxin concentrations were below the limit of detection (LOD), but the taste-and-odor compounds 2-methylisoborneol (2-MIB) and geosmin were detected at concentrations of 34.2 ng/L and 21.5 ng/L, respectively.Extreme low-water and high-temperature conditions reduced water flow and concentrated nutrients, which were the main triggers of the cyanobacterial bloom. As a result, water supply costs increased significantly for most water treatment plants. Conventional treatment processes have limited capacity to remove algae and taste-and-odor compounds, placing considerable pressure on ensuring the safety of drinking water supply.【Conclusions】Based on the water treatment plant survey, water quality and aquatic ecological monitoring results, this paper proposes management strategies in terms of water resource dispatch, enhancement of emergency treatment capacity at water treatment plants, and simultaneous monitoring of hydrological, water quality, and aquatic ecological parameters, early warning of cyanobacterial blooms, and prevention and control of cyanobacterial blooms. The above work is expected to provide a scientific basis and practical reference for ensuring water supply safety and preventing and controlling cyanobacterial blooms in the middle and lower reaches of the Han River Basin under extreme hydro-meteorological conditions.