Marblehead is the oldest lighthouse in continuous operation on the United States side of the Great Lakes. It has guided sailors safely along the rocky shores of Marblehead Peninsula since 1822, and is an active aid to navigation. The Ohio Department of Natural Resources has maintained the property surrounding the lighthouse since 1972 and accepted ownership of the Marblehead Lighthouse tower in May 1998. The U.S. Coast Guard continues to operate and maintain the lighthouse beacon. Today’s 300 mm lens projects a green signal that flashes every six seconds and is visible for 11 nautical miles (20 km). The distinctive green distinguishes the lighthouse signal from white lights coming from air beacons.