Abstract: A shroud for an impeller used for aeration of contaminated water, has a front portion for a propeller, behind it is a rear portion with separate apertures for water and air, the air aperture accommodates the propeller shaft. A draft tube connected to the shroud has a stub tube at the rear end for air ingress. The propeller shaft passes through the draft tube, and a bearing box to a motor. The draft tube has a rear attachment plate to which the bearing box is attached. The bearing box has a bearing for the shaft held in place by a retainer, it also is attached at its rear to a motor mounting plate, on which the motor is mounted. The impeller is mounted on a swivel arm mounted pivotally on a frame, typically on a raft. The swivel arm allows the impeller to be positioned angularly and lockably in a plurality of angular positions from horizontal to vertical.