President Obama on Tuesday formally blocked offshore oil and gas drilling in most of the Arctic Ocean, answering a call from environmentalists who say the government needs to do more to prevent drilling in environmentally sensitive areas of U.S.-controlled oceans.

Obama is invoking a 1953 law governing the Outer Continental Shelf to block drilling in federal waters in the Arctic's Chukchi Sea and most of its Beaufort Sea. He also protected 21 underwater canyons in the Atlantic Ocean from drilling, White House officials said Tuesday.

Canada will block drilling in all of its Arctic Ocean acreage, a moratorium officials will review every five years, the White House said.

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“These actions, and Canada’s parallel actions, protect a sensitive and unique ecosystem that is unlike any other region on Earth,” Obama said in a statement.

“They reflect the scientific assessment that, even with the high safety standards that both our countries have put in place, the risks of an oil spill in this region are significant and our ability to clean up from a spill in the region’s harsh conditions is limited.”

The announcement locks in a decision Obama made last month to block drilling in the Atlantic and Arctic Oceans during an offshore leasing plan that runs through 2022.

It also cements Obama’s legacy as a president who has taken aggressive unilateral action against climate change and protected more land and water than any previous president.

Environmentalists supported Obama’s November leasing plan, but many said he needed to go further and block drilling in the Atlantic and Arctic Oceans once and for all.

The oil and gas industry is certain to push lawmakers to reverse Tuesday’s decision.

U.S. acreage in the Arctic is estimated to contain 27 billion barrels of oil and 132 trillion cubic feet of natural gas.

The industry has opposed government efforts to block drilling there, saying the U.S. will hurt the rural Alaskan economy if it prevents oil production, and also cede an economic advantage to other Arctic countries like Russia, which has more relaxed rules on drilling.

Tuesday’s announcement does leave 2.8 billion acres of the Beaufort Sea near Alaskan state waters open to leasing. The White House said that area is close enough to existing drilling infrastructure that “the president deemed it prudent to leave that area for further study and further consideration.”

There is no traditional drilling industry in federal waters in either the Arctic or Atlantic oceans, and many companies that own drilling leases in the Arctic have yielded them in the face of low oil prices globally.

In his statement, Obama said the oil market makes now an acceptable time to block off future drilling.

“It would take decades to fully develop the production infrastructure necessary for any large-scale oil and gas leasing production in the region — at a time when we need to continue to move decisively away from fossil fuels,” he said.

The Gulf of Mexico is the hotbed for the American offshore drilling industry, and Obama’s 2017-2022 leasing plan allows for more drilling there.