The invention relates to a horizontal agitator for producing a flow in a clarifier, a submersible motor and a propeller drivingly connected thereto forming an assembly unit, wherein a receiving portion for removably attaching the assembly unit is provided and can be supported on the bottom of the clarifier, and wherein a guide for guiding the assembly unit along a substantially vertical movement path between a surfacing position above a maximum nominal sewage level defined for the clarifier and the receiving portion is provided. In order to improve the efficiency of the horizontal agitator and to reduce complexity of manufacture, the guide is formed by at least one first cable extending between the surfacing position and the receiving portion.