The US President George W Bush is to announce the creation of the world's largest marine protection area spanning half a million square kilometres.
The three areas to be designated as marine national monuments include the Mariana Trench and Northern Mariana Islands, the Rose Atoll in American Samoa and a chain of remote islands in the Central Pacific.
Establishing the reserves aims to ensure that certain resources are protected, such as rare fish and bird species, coral reefs and underwater active volcanoes.
The Marianas Trench includes submerged active volcanoes and hydrothermal vents and the deepest point on Earth.
The Pacific Remote Islands National Monument will comprise seven areas: Kingman Reef; Palmyra Atoll; Howland, Baker and Jarvis Islands; Johnston Atoll and Wake Island.
Collectively, the three areas will nudge out the Phoenix Island Protected Area, which Kiribati established last year as the world's largest protected area.
They also top Mr Bush's last such announcement of a marine protection area in 2006 - the 363,000 square kilometers of Pacific Ocean near the northwestern Hawaiian islands.