Trapped common carp (Cyprinus carpio) display a pronounced escape behaviour ofjumping out of the water; this behaviour is not exhibited by most Australian native fishes. Hence,there appears to be an important opportunity to exploit the unique jumping behaviour of nonnativecommon carp to aid selective removal. We report on the Williams cage, a simple device thatautomatically separates jumping common carp from nonjumping fish. Between November 2002and April 2005, the Williams cage was tested at Torrumbarry Weir fishway on the Murray River,Victoria, Australia, and trapped fish were counted every 24 h. The Williams cage successfullyseparated 88% of adult common carp into a confinement area. In contrast, more than 99.9% of8,031 native fish passed through the Williams cage and exited the fishway. The Williams cagemay provide a method for controlling dispersal and abundance of common carp and may beapplicable to other nuisance fish species.