NEW YORK—The National Geographic Society announced a major expansion Monday of its campaign to help protect the planet's most species-rich marine areas, with a goal of convincing governments to officially safeguard more than 770,000 square miles (two million square kilometers) of ocean.

The Society aims to help designate more than 20 new underwater locales as marine reserves in the next five years.

"Preserving our oceans is essential for protecting biodiversity," former President Bill Clinton said as he announced the Society's efforts at the Clinton Global Initiative in New York on Monday.

"The ocean is the world's largest natural resource," Clinton said, noting that it contributes more than $20 trillion to the global economy. Yet, "human impact on the ocean is undeniable."

The expanded effort will build on National Geographic's Pristine Seas project, which has financed 10 scientific expeditions to remote areas of ocean around the world, including in the South Pacific and off Africa, Russia, and South America. New efforts will target the Seychelles—an archipelago in the Indian Ocean—northern Greenland, and South America's Patagonia region, Clinton said.

As a result of the program's work, government leaders have protected areas in the United States, Chile, Kiribati, and Costa Rica that cover more than 150,000 square miles (about 400,000 square kilometers).

"A few country leaders have already shown tremendous leadership in ocean conservation by creating the largest marine no-take areas in history," says Enric Sala, a National Geographic Explorer-in-Residence who launched Pristine Seas in 2009.

"National Geographic Pristine Seas and our partners are excited to inspire other leaders to protect what's irreplaceable: the last wild places in the ocean."

Terry Garcia, National Geographic's chief science and exploration officer, pointed to overfishing, pollution, and climate change as major threats facing the ocean.

View Images Blacktip sharks, bluefin trevallies, and twinspot snappers swim in a lagoon off Caroline Island, also called Millennium Island. Photograph by Brian Skerry, National Geographic

If the campaign is successful, it will help countries meet the United Nations Convention on Biological Diversity's target of protecting 10 percent of the world's oceans by 2020.

The Pristine Seas team is already working with national governments to help them create several new marine reserves. One would expand the Pacific Remote Islands Marine National Monument in U.S. waters, making it the largest region of protected area anywhere in the world, on land or sea.

Another Pristine Seas project would create a reserve around the United Kingdom's Pitcairn Islands.

Partners announced for Pristine Seas include the Waitt Foundation, Prince Albert of Monaco, the Leonardo DiCaprio Foundation, the Jynwel Foundation, the Leona and Harry Helmsley Charitable Trust, Blancpain, Davidoff Cool Water, Lindblad Expeditions, Dynamic Planet, former President José María Figueres of Costa Rica, and individual donors.