(Jim Maragos/USFWS/AP Photo)

President Obama today will sign a proclamation creating the largest marine reserve in the world - three times the size of California, totaling 490,000 square miles.

The move is a six-fold expansion of the existing Pacific Remote Islands Marine National Monument, which covers several small U.S.-controlled islands and atolls in the central Pacific to the west of Hawaii. It's existing size is just 87,000 square miles.

The designation bans commercial fishing, dumping and mining in the national monument's waters, home to "deep coral reefs, seamounts, and marine ecosystems unique to this part of the world among the most vulnerable areas to the impacts of climate change," according to the White House. Environmental groups are calling this a "historic" move to protect precious wildlife.

Visualize our fantastic expanded monuments - now the largest protected area on EARTH! #monumentsmatter #MPAs #PRIMNM pic.twitter.com/KGm2gDcrT8

- Marine Conservation (@savingoceans) September 25, 2014

With more than 100 wilderness requests mired in Congress, Obama has repeatedly taken executive action on his own. He has used his authority to designate more acres of federal land and sea environmentally-protected areas than any other president in the last five decades.