The geometry of ${\mathrm{H}}_3{\mathrm{O}}^{+}$ion is

The shape of ${\mathrm{H}}_3{\mathrm{O}}^{+}$  is pyramidal as the 3 hydrogen atoms lie at three corners of oxygen as a triangle, and one lone pair of electron on oxygen attains pyramidal shape to ${\mathrm{H}}_3{\mathrm{O}}^{+}$.