A quiescently flush resilient portion of a water jet exit channel that distends under controlled fluidic pressure to narrow the flow channel to trade off power for speed in a water-jet-powered watercraft and/or to suppress impeller cavitations during standing starts. The resilient portion may be a continuous annular portion or may be segmented for thrust vectoring. The resilient portion may be built into a water jet exit channel or may be in an add-on nozzle that can be attached to the water jet exit channel, especially for aftermarket improvements. The control system, the water jet exit structure, the water jet, and the watercraft and included. A resilient ring with top and bottom radially outwardly extending flanges mounted on a rigid ring and compressed within a canister between an annular canister floor and a compressive annular cap may provide the plenum and resilient portion of the water jet exit channel.