President Obama used a presidential proclamation to create the world’s largest protected marine area Thursday, the White House announced in a press release.

Areas around U.S.-controlled islands and atolls will be added to the Pacific Remote Islands Marine National Monument, created by President Bush in 2009. The monument will expand to almost 500,000 miles—six times its current size, and larger than California. Fishing, undersea mining, and other commercial activity will be banned in the protected area.

This is the 12th time President Obama used his presidential powers to set aside areas for environmental protection, and environmental activists are pleased. “This is a great moment,” Greg Stone, chief scientist for Conservation International, told the Guardian. “This is some of the last real tropical ocean wilderness left on the planet, so it’s good to put some of these kind of reef systems aside.”