  We report non-local electrical measurements in a mesoscopic size
two-dimensional (2D) electron gas in a GaAs quantum well in a hydrodynamic
regime. Viscous electric flow is expected to be dominant when electron-electron
collisions occur more often than the impurity or phonon scattering events. We
observe a negative nonlocal resistance and attribute it to the formation of
whirlpools in the electron flow. We use the different nonlocal transport
geometries and compare the results with a theory demonstrating the significance
of hydrodynamics in mesoscopic samples.
