The United States' nearly 1,800 marine protected areas contain some of the country's most spectacular reefs, underwater archaeological sites and most valuable commercial fisheries and tourist diving sites.
Ranging in size from less than one square mile (2.6 square kilometers) to over 5,300 square miles (13,700 square kilometers), the sites pepper the Pacific and Atlantic Oceans, as well as the East and West Coasts.
The U.S. commonwealth of the Northern Mariana Islands—made up of 14 islands that span 183 square miles (475 square kilometers) in the North Pacific Ocean—was designated the U.S. Mariana Trench Marine National Monument in January 2009.
Formed by underwater volcanoes, the southernmost of these islands have some of the oldest coral reefs along the island chain. The reef off of Saipan Island is the most diverse.