Manchac is located on Lake Maurepas on the Pass Manchac waterway, which connects to Lake Pontchartrain. It is home to the ruins of one of the five lighthouses set up for Lake Pontchartrain, the Pass Manchac Light. The last lighthouse to be built on the north side of the entrance to Pass Manchac (the fourth one on that site) was completed in 1857. It was automated in 1941, and the dwelling was razed in 1952; the U.S. Coast Guard decommissioned the light and abandoned the property in 1987.