Drilling for new oil and gas reserves has been banned in US waters in the Atlantic and Arctic Oceans by Barack Obama.
The move is being seen as an attempt by the outgoing president to leave his mark in protecting the environment before Donald Trump takes office – even though few energy companies have sought to drill anytime soon in those areas. Exploratory drilling in the Arctic is expensive and risky.
The ban affects 46.5 million hectares of federal waters off Alaska in the Chukchi Sea and most of the Beaufort Sea, and 1.5 million hectares in the Atlantic from New England to Chesapeake bay.
Canada has also announced similar plans for its own Arctic waters, in a joint commitment with Washington.
Obama used a 1950s law that allows presidents to limit areas from mineral leasing and drilling.
He cited studies saying the risks of an oil spill in the region are significant, and the ability to deal with one limited.
The effects of the 1989 Exxon Valdez tanker spill in Alaska are still felt today.
The incoming president-elect has said he would expand offshore oil and gas drilling, promising to take advantage of existing US reserves.
Environmental groups say Trump would have to go to court to overturn the permanent nature of the ban. This has been disputed by the American Petroleum Institute oil industry group, which says it hopes the incoming administration will reverse the decision.