The tug Ken MacKenzie pushing a barge loaded with gravel on the Fraser River struck a railroad bridge that connects Queensbourh to New Westminster near Vancouver, British Columbia, Canada.    The pair of vessels were heading downstream with it struck the swing bridge causing damage the pivot mechanism.    This has the swing bridge is stuck open and is out of service.  River traffic was halted as the barge was kept wedged against the bridge until the bridge can be stabilized.   Conditions on the Fraser was reported as having an average freshet, but is not out of the ordinary and was not the cause of the accident.  Reports state no one was injured and no pollution was released.  Government authorities are conducting an investigation into the incident.