Lakes undergo a transition from a macrophyte-dominated state to a phytoplankton-dominated state, accompanied by an increase in nutrient loads, a decline of aquatic vegetation (AV), and the proliferation of phytoplankton. Once the regime shift occurs, it is difficult to reverse, seriously affecting the ecological functions and service values of the lake ecosystem. Identifying tipping points and analyzing the process of lake regime shifts can help predict potential ecological risks, providing decision support for lake ecological protection, restoration, and integrated management. In this study, we took Lake Liangzi as an example to analyze water environmental changes, to identify the tipping points of AV, and to investigate the process of lake state shifts. For this purpose, a long-term dataset of AV and algal bloom (AB) was interpreted from remote sensing data, and combined with long-term data of key water environmental factors. Over the past 34 years (1990-2023), the ecosystem of Lake Liangzi had undergone significant changes. Lake water quality gradually deteriorated from 1990 to 2017. A sharp shift in transparency occurred in 2010, followed by abrupt changes in permanganate index and total nitrogen in 2011, and total phosphorus in 2017. The critical year for the lakes state shift occurred in 2016, with a shift in AV coverage, especially in submerged aquatic vegetation (SAV), indicating the collapse of the AV-dominated state. During 2017-2023, the AV dramatically declined, and there were AB outbreaks in 2022-2023, suggesting that the lake was transitioned to a phytoplankton-dominated ecosystem. Integrating the shift periods of various factors, the regime shifts in Lake Liangzi could be divided into four stages, i.e., the macrophyte-dominated state (before 2010), significant increase of nutrient load (2011-2016), degradation of AV (2017-2021), and phytoplankton-dominated state (2022-2023). Our approach and findings provided theoretical support for ecological restoration and management decisions for Lake Liangzi. They also offered scientific reference for the early warning, restoration, and management of other shallow lakes in the middle and lower reaches of the Yangtze River.