An improved fluid mixing apparatus is disclosed for the mechanical mixing of fluids or solids-laden slurries contained within a vessel. The invention utilizes a fluid driven turbine to drive a submerged mixing impeller through a speed reducing gearbox. A fluid conducting stator houses one or more turbine blade row(s) that are rotated as a working fluid is pumped through the turbine section by an external pump that circulates fluid at the required flow rate and head. The turbine shaft is rigidly connected to the high speed input shaft of a speed reducing gear box. The low speed output of the gearbox is rigidly attached to submerged mixing impeller(s).