Cocos Lagoon appears as a small incomplete coral

Coral

Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

 atoll

Atoll

An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...

 attached to the southwestern coast of Guam

Guam

Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

 in the area of the village

Municipality

A municipality is essentially an urban administrative division having corporate status and usually powers of self-government. It can also be used to mean the governing body of a municipality. A municipality is a general-purpose administrative subdivision, as opposed to a special-purpose district...

of Merizo

Merizo, Guam

Merizo , is the southernmost village in Guam, a U.S. territory. Cocos Island is a part of the municipality. The village's population has decreased since the island's 2000 census. - History :...

. It stretches about 5.5 km east-west and 3.5 km north-south, covering an area of more than 10 km².

Cocos Island and Babe Island

Babe Island

Babe Island is an island which lies in the entrance to Cobblers Cove, along the north coast of South Georgia. It was charted and named by DI personnel in 1929....

 sit atop the southern portion of the Merizo Barrier Reef and separate Cocos Lagoon from the open ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 in the south. In the east, Cocos Lagoon is separated from Achang Reef by narrow Manell Channel that leads to Achang Bay. In the northwest, Mamaon Channel separates Cocos Lagoon from the main island of Guam and allows boat access to Merizo. Southeastward of the channel, down to Achang Bay, there is no separation to the main island of Guam. Along the west side, the barrier reef uncovers in spots but has no islands.