A rotary sprinkler comprises a body and a rotor. The body has an inlet bore, an outlet bore, and an internal cavity therebetween. The inlet bore has an upstream end connectable to a water supply pipe and a downstream end formed as a jet nozzle. The outlet bore has an upstream end with a rim. The rotor has an axially extending shaft with an axial shaft channel and at least one vane with a vane channel extending away from the shaft and having an outlet constituting an outlet of the sprinkler. The shaft channel and the vane channel define a smooth water flow passage having an open cross-section. The shaft is inserted in the outlet bore of the body to enable free rotation of the rotor. The sprinkler further comprises a retaining ring that is assembled to the upstream end of the shaft of the rotor, is disposed in the internal cavity of the sprinkler body, and is adapted to abut the rim of the outlet bore, thereby carrying axial forces applied to the rotor.