We consider the excitation, nonlinear evolution and saturation of a single coherent mode in a turbulent plasma background. We adopt a generic wave-kinetic description of plasma turbulence, based on a Wigner–Moyal equation, which stays valid well beyond the geometric optics approximation. We illustrate our model by considering the case of a geodesic acoustic mode in a tokamak plasma, in the presence of a broad spectrum of drift wave turbulence.