evidence: Serranilla Bank is an atoll in the southeastern Caribean. It is approximately 400 kilometres (250 mi) northeast of Nicaragua. Only the eastern and southern part of the reef are visible. The bank is made up of several cays, and has a size of about 45 kilometres (28 mi) by 37 kilometres (23 mi). It covers an area of about 1,200 square kilometres (460 sq mi).Many parts of the coral reef are dry at low tide. The ocean has a depth of between 9 metres (30 ft) and 37 metres (121 ft) in most parts.