President Barack Obama has imposed a permanent ban on oil and gas drilling in most US-owned waters in the Arctic Ocean.
The move, which also includes certain areas of the Atlantic Ocean, comes a month before Donald Trump becomes president promising to unleash the nation's untapped energy reserves.
The White House announced the actions in conjunction with Canadian Prime Minister Justin Trudeau, who also placed a moratorium on new oil and gas leasing in its Arctic waters, subject to periodic review.
Mr Obama is making use of an arcane provision in a 1953 law to ban offshore leases in the waters permanently. The statute says "the president of the United States may, from time to time, withdraw from disposition any of the unleased lands of the outer Continental Shelf".
Environmental groups hope the ban, despite relying on executive powers, will be difficult for future presidents to reverse.
The White House is confident the president's order will withstand legal challenge and said the language of the statute provides no authority for subsequent presidents to undo permanent withdrawals.
The Atlantic waters placed off limits to new oil and gas leasing are 31 canyons stretching off the coast of New England south to Virginia, though some had hoped for a more extensive ban that would have extended further south.
Existing leases are not affected by the president's executive actions.
The administration cited environmental concerns in both regions to justify the moratorium. Mr Obama also noted the importance of the Chukchi and Beaufort seas in providing subsistence for native Alaskans and the vulnerability of the ecosystem to an oil spill to justify his directive.
Mr Obama said just 0.1% of offshore crude production came from the Arctic in 2015, and at current oil prices, significant production would not occur in future decades.
Industry officials accused Mr Obama of "last minute political rhetoric".
"Instead of building on our nation's position as a global energy leader, today's unilateral mandate could put America back on a path of energy dependence for decades to come," said Dan Naatz of the Independent Petroleum Association of America.
Governor Bill Walker of Alaska, an independent, said Mr Obama's move marginalised local voices.
In issuing a permanent ban, the president appears to be trying to tie the hands of his successor. Mr Trump has vowed a domestic energy revolution and is filling his Cabinet with nominees deeply opposed to Mr Obama's environmental and climate change actions.
Environmental groups were calling for a permanent ban even before the presidential election, but Mr Trump's victory has provided greater urgency for them and for businesses that rely on tourism and fishing.
Mr Trump has said he intends to use all available fuel reserves for energy self-sufficiency - and that it is time to open up offshore drilling.
"This decision will help protect existing lucrative coastal tourism and fishing businesses from offshore drilling, which promises smaller, short-lived returns and threatens coastal livelihoods," said Jacqueline Savitz of the advocacy group Oceana.
A key question to be answered is how difficult it will be for future presidents to overturn Mr Obama's decision should they seek to do so.
Advocacy groups warned they will fight to protect the ban during future administrations.
"If Donald Trump tries to reverse President Obama's withdrawals, he will find himself in court," said Marissa Knodel of Friends of the Earth.
The decision came as Mr Obama spends the Christmas holidays in Hawaii.
Some Democratic politicians applauded him, while some Republicans were highly critical.
"As President-elect Trump nominates fossil fuel allies to his Cabinet, President Obama has instead put the interests of millions of Americans ahead of those of Big Oil with these permanent protections," said Democratic Senator Ed Markey of Massachusetts.
"The extremes to which this president will go to appease special interests never ceases to amaze," countered Utah Republican Rob Bishop, chairman of the House Committee on Natural Resources.
"This is not a moral calling; it's an abuse of power."