The 45 meter long, 538 gt tug Bulwark went aground in Nelson Bay, Alaska.  The tug was attempting to anchor a barge when the tug struck bottom.   The Bulwark was able to refloat itself later the same day.   No reports of injuries, damage or pollution being released.   The Bulwark remained anchored awaiting divers to conduct a survey of the vessel.   The Coast Guard is conducting an investigation into the incident.