Abstract: A pond pump having a housing (1) enclosing a synchronous motor (9) with a drive shaft (40) on which an impeller (20) is loosely fitted so that, on start up, the shaft (40) can rotate relative to the impeller (20) until a pair of diametrically opposed keyways (43) on the shaft engage and entrain keyways (27) on the impeller (20) to rotate it continuously in one direction. If the drive shaft initially rotates in the opposite direction, pegs (25) on the rear face of the impeller (20) engage with a detent (60) located behind the impeller (20) to stop said rotation until the motor (9) restarts and rotates the drive shaft (43) in said first direction. One end of the drive shaft (40) is received in a first bearing (50) mounted in the housing (1), the other end of said shaft being received in a blind bore (28) in the impeller (20) which is coaxial with the axis of rotation of the shaft (40).