Middleton Reef is a coral reef in the Coral Sea. It is separated by a deep oceanic pass some 47 km wide from nearby Elizabeth Reef, forming part of the Lord Howe Rise underwater plateau. It is around 230 km from Lord Howe Island and 555 km from the coast of New South Wales. In 1997 the Environment, Sport and Territories Legislation Amendment Bill 1996 included the reef in Australia's Coral Sea Islands Territory. It is about 8.9 km long by 6.3 km wide. At low tide most of the reef flat is exposed, at high tide only one cay is visible, The Sound, 100 m by 70 m and one metre above sea level.