There have been U.S. presidents with sea legs—picture JFK at the helm of his beloved yacht Honey Fitz—but few who can challenge the oceanic affinity of President Obama, a child of the Pacific raised in Hawaii and Indonesia. So it’s no surprise that in 2014, invoking the Antiquities Act of 1906, he expanded the Pacific Remote Islands Marine National Monument—southwest of Hawaii—to six times its current size. At 490,000 square miles, it is now the largest marine reserve in the world, protected from the damage of pollution, commercial fishing, and resource extraction. His administration, arguably the most ecologically engaged in American history, has hinted that he might cordon off two new marine reserves in the Atlantic. And while fishing interests have blocked the creation of one of them, Cashes Ledge, environmentalists still hold out hope that Obama may designate the second, known as New England Coral Canyons and Seamounts, in a parting gesture.