Frederick Reef is in the Coral Sea Islands, over 220 nautical miles (410 km) northeast of Gladstone, Queensland. The reef gets its name from Frederick, which first reported sighting the reef. Frederick Reef is a small atoll with a large rock called Ridge Rock at the southern end, a sand cay called Observatory Cay, and a lighthouse at the northern end, which is the only permanently dry land, although there are a few of others cays that can be awash at high tide. The reef is around 30km2. The reef is located in some deep water and drops sharply to over 2,500 metres (8,200 ft) on the western side.