For over one hundred years, presidents of both parties have used executive power to protect America’s lands and waters. Until the second half of the twentieth century, however, little attention was given to protecting the marine ecosystem. Federal authority reaches out to two hundred miles or more in the oceans off the United States, covering an area known as the Outer Continental Shelf. Federal interest in the area historically focused on developing oil and gas reserves and ensuring that the area was open to trade and commerce. The area is also very important for indigenous subsistence uses and commercial and sport fisheries. Yet it has received scant attention from Congress in terms of environmental protection. Climate change and ocean acidification have increased recognition of the marine ecosystem’s importance to the overall health of the planet. This Article reviews President Obama’s recent withdrawal of swaths of the outer continental shelf from oil and gas leasing under the Outer Continental Shelf Lands Act. It argues that while Congress has paramount authority over the outer continental shelf and retains the authority to undo conservation actions, it has delegated limited conservation authority to the president under section 12(a) of the Act. Thus, President Obama’s recent protective measures taken under the Act may only be altered by Congress—not by a subsequent president. This Article compares the president’s withdrawal authority under the Outer Continental Shelf Lands Act to the president’s authority to establish national monuments under the Antiquities Act. It argues that Congress did not delegate power to revoke national monument designations under the Antiquities Act, nor permanent withdrawals under section 12(a) of the Outer Continental Shelf Lands Act.