We investigate the role of the fountain effect and plasma bubbles for the formation of the large equatorial plasma depletions during the geomagnetic storm of 15 July 2000. The large equatorial plasma depletions are detected in the Atlantic sector on the night of the 15th by the Defense Meteorological Satellite Program (DMSP) F15 and the first Republic of China Satellite (ROCSAT-1). The observations show discontinuous drop of the plasma density at the walls of the depletions, flat plasma density inside the depletions, and persistence or growth of the depletions over night. These properties are not consistent with the trough morphology induced by the fountain effect. The coincident ionospheric observations of DMSP F15 and ROCSAT-1 demonstrate that the large depletions are created in the longitude regions where plasma bubbles are present. The occurrence of the large depletions after sunset, elongation in the north-south direction, formation of steep walls, and colocation with plasma bubbles at lower altitudes or earlier times suggest that the large depletions are closely associated with plasma bubbles.