Personal watercraft systems and watercraft power systems are described. The personal watercraft power systems include a housing for supporting a water jet pump and engine system. The housing is constructed to support the power system and removably engage a watercraft. An engine and a centrifugal pump are enclosed in the housing and operatively connected by an endless drive, such as a belt. A crankshaft of the engine is generally aligned and offset for a pump shaft of the centrifugal pump. An impeller is connected to the pump shaft and is constructed in rotate in a plane generally aligned, and preferably offset from, a plane of a water surface. The orientation of the engine and the centrifugal pump provides a watercraft power system that has a reduced profile and is particularly applicable for watercraft constructed to support an operator in a prone position. The housing is constructed to removably engage a number of watercraft configurations and provides a watercraft power system that is easily serviceable, highly versatile and dynamic.