The experimentally observed features of the spectra of the geodesic acoustic modes (GAMs) in tokamaks, such as GAM’s modulation, peak splitting, intermittency and other, have no satisfactory explanations within the framework of standard theory. To fill in this gap, the fluid model, which describes the consistent dynamics of the GAMs and low-frequency zonal flow (ZF), is developed. The linear approximation of the model exhibits two eigenmodes of vastly different frequencies, GAM and ZF, while the nonlinearity results in a much richer spectral pattern, which qualitatively corresponds to the experimental observations.