A rotary machine for mixing, pumping or agitating a fluid includes an impeller for acting on the fluid, a drive unit for rotating the impeller around a rotation axis, a drive shaft connecting the impeller with the drive unit, a mounting flange for fastening the rotary machine to a wall of a vessel, and a support structure for supporting the rotary machine, the support structure comprising at least one leg, each leg extending in a vertical plane from a first end along a longitudinal axis to a second end, each leg including an outer member and an inner member coaxially arranged in the outer member, and the inner member slidingly movable relative to the outer member for adjusting the length of the respective leg. In addition, a method of mounting a rotary machine for mixing, pumping or agitating a fluid to a wall of a vessel is proposed.