Key dates: Aug. 2, medal events Venue: Lee Valley White Water Centre Big story: Two-time defending gold medalist Elena Kaliska won't defend her title after failing to qualify. Top U.S. prospects: Caroline Queen overcame a serious knee injury in 2009 to qualify for her first Games. Others to watch: Jana Dukatova of Slovakia has dominated at world and European championships but is seeking her first Olympic medal. Corinna Kuhnle of Austria is a rising star who won gold at last year's World Championships. Little-known fact: When this sport made its debut in 1932, it was staged on flatwater instead of whitewater rapids.