The Portsmouth Harbor Light with the Whaleback Lighthouse in the background. Whaleback marks the approach to the harbor of Portsmouth, New Hampshire, and has often been referred to as a New Hampshire lighthouse, but this rugged granite tower is clearly is in Maine waters by about 1500 feet. The jagged ledge known as Whaleback lurks menacingly on the northeast side of the entrance to the Piscataqua River, approximately a half -mile south of Gerrish Island, part of the town of Kittery. The ledge, which is completely underwater at high tide, is, in fact, a continuation of the southern point of Gerrish Island. Portsmouth Harbor Lighthouse is located within Fort Constitution in New Castle, New Hampshire, USA. The station was established in 1771 and was the 10th of 11 light stations established prior to the American Revolution. The first tower was a shingled wooden structure with an iron lantern and copper roof. Its light source was three copper oil lamps. The first tower was replaced in 1804 by an 80-foot (24 m) octagonal wooden tower approximately 100 yards (91 m) east of the 1771 tower. In 1851, twenty years after the establishment of Whaleback Lighthouse, the tower was shortened to 55 feet (17 m). Three years later, in 1854, the tower was fitted with a Fourth (4th) Order Fresnel Lens. In 1878, a new 48-foot (15 m) cast-iron, brick-lined lighthouse tower was erected on the same foundation as the 1804 tower. When the new tower was completed, the surrounding remains of the 1804 tower were removed. The current light is a fixed green signal that is visible for 12 nautical miles (22 km). The light is made green by an acrylic cylinder that surrounds the lens. Other structures at the light station that are still standing are the 1903 oil house (restored in 2004) and the 1872 keeper's house (currently United States Coast Guard offices). On October 8, 2009, Portsmouth Harbor Lighthouse was listed on the National Register of Historic Places.