A submerged dock lays off the Fort McHenry National Monument, in the Patapsco River, Baltimore MD—and a well-known marked hazard zone. The depth surrounding the object is navigable at depths greater than 30 feet. Just over the hazard, depths are only 5-8 feet, making it impossible for a traditional survey vessel to navigate. We chose this particular location to demonstrate how an ultra-high resolution multibeam sonar can be used in conjunction with a small autonomous surface vehicle (ASV) to obtain a more complete survey of a complex and challenging area.