Groundwater level change can influence SHM measurements and cause faulty structural damage identification using vibration-based methods. The aim of this paper is to analyse the impact of the groundwater level changes on the modal parameters of the mid-rise reinforced buildings. The modal parameters of the mid-rise reinforced buildings are determined using finite element models (FEM). Three different FE models of structural system types of nine-story reinforced (RC) buildings with shallow foundations are used to determine the impact of groundwater level fluctuation on the values of the natural frequencies of the buildings. Changes of the groundwater level have an impact on the natural frequencies of the mid-rise reinforced buildings. It is found that groundwater level rise causes decrease in the natural frequency value. In this research it is estab-lished that environmental variable conditions can change abruptly and there is a nonlinear cor-relation between groundwater level change and natural frequencies of the buildings. The natural frequencies of the buildings can change under varying environmental conditions as well as in the case of structural damage. In order to identify the structural damage in long term SHM meas-urements, features that are sensitive to structural damage, but are not affected by the changes of environmental and operational conditions must be selected. Data normalisation and elimination using linear correlation methods can be used for short-term SHM monitoring under varying seasonal groundwater level change.