The variation of hydrological processes has been extensively discussed worldwide, yet little is known about the relative impact of human activities, and the precipitation–water level relationship in urbanized, watery areas. Thus, the change in water level and the influential variables are analysed for 1960–2014 in the urbanized and watery Taihu Basin, China. The results indicate that the water level displays a significant increasing trend. Furthermore, low-oscillation and high-oscillation periods were found to have occurred in the 1960s–1970s and 2000s, respectively, by the quantile perturbation method. A strong relationship was shown between water level and precipitation in the 1960s–1980s, especially in the flood season. Since then, human activities, such as land-use change, river system degradation and hydrological structures, have played distinct roles and caused more than 82% of the annual and flood-seasonal water level variation. The results may provide a more comprehensive understanding of the hydrological processes and provide a good reference for flood control.