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This paper presents the manipulation of microspheres under water by use of an untethered electromagnetically actuated magnetic microrobot (Mag-muBot), with dimensions 250 times 130 times 100 mum<sup>3</sup>. Manipulation is achieved by two means: contact and noncontact pushing modes. In contact manipulation, the Mag-muBot is used to physically push the microspheres. In noncontact manipulation, the fluid flow generated by the translation of the Mag-muBot is used to push the microspheres. Modeling of the system is performed, taking into account micrometer-scale surface forces and fluid drag effects to determine the motion of a sphere within a robot-generated fluid flow. Fluid drag models for free-stream flow and formulations for near-wall flow are both analyzed and compared with the experiments, in which pushing of two sphere sizes, i.e., 50 and 230 mum diameters, is characterized in a controlled, robot-generated flow. Dynamic simulations are provided using the developed physical models to capture this behavior. We find that the near-wall physical models are, in general, in agreement with the experiment, and free-stream models overestimate microsphere motion.