Forced and free oscillations of water level were recorded in well YuZ-5, Kamchatka due to the passage of seismic waves from the Sumatra-Andaman earthquake of December 26, 2004, Mw = 9.3, hypocentral distance 8250 km. The greatest amplitude of water level oscillations, at least 5 cm, was observed during the onset of seismic surface waves with a typical period of 20–50 s. The total duration of the forced and free water-level oscillations was about ten hours. The available theoretical models that describe oscillations were used to estimate the transmissivity of the groundwater reservoir. A hypothesis was proposed to explain a temporary increase in reservoir transmissivity during the passage of seismic waves by invoking defective structure of the crack-pore space and a sharp increase in host rock permeability.