Out along Derby Wharf in Salem, the white square tower of Derby Wharf Light Station marks the end of your walk onto the water. It was built in 1871 and was added to the National Register of Historic Places in 1987. The United States Coast Guard Light List description reads "White square tower. Maintained by the U.S. Park Service." The actual light is 25 feet above Mean High Water, and its red light is visible for 4 nautical miles (7.4 km; 4.6 mi).
When first built in 1871 the station used an oil lamp shining through a Fresnel lens; for many years Derby Wharf Light had one of only 17 sixth-order Fresnel lenses in the United States. Today the light is solar powered, and it gives a red flash every six seconds. Measured at 25 feet above Mean High Water, the lantern's red glow reaches 7.4 kilometers, about 4.6 miles, across the water.
Stand close and you can see the white square tower the Coast Guard describes and the lantern where the red flash still marks the night. Notice that lantern and the Derby Waterfront stretching just beyond it.