President Obama announced on Tuesday a ban on oil and gas drilling in the Arctic and along the Atlantic coast from Virginia to Maine, a move that would protect more than one hundred million acres of federal land as a last-ditch effort to shore up and preserve Obama’s environmental legacy before Donald Trump takes office in January. The ban on 98 percent of federally owned Arctic waters was negotiated and enacted alongside a similar ban in the Canadian Arctic signed by Canadian Prime Minister Justin Trudeau.

“These actions, and Canada’s parallel actions, protect a sensitive and unique ecosystem that is unlike any other region on earth,” the 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 executive action prohibiting offshore drilling relies on so-far untested legal reasoning rooted in the 1953 Outer Continental Shelf Lands Act. “The 1953 law, which governs how the executive branch uses and leases federal waters for offshore energy exploration, includes a provision that allows presidents to put those waters off-limits to oil and gas drilling,” according to the New York Times. “Presidents Dwight D. Eisenhower, Richard M. Nixon and Bill Clinton used the law to protect sections of the Atlantic, Pacific and Arctic Oceans, but those protections came with time limits, usually one to two decades.”

The Obama measure, however, is intended to be permanent although it’s not altogether clear how that will hold up under a new president and Republican-controlled congress or legal scrutiny when it inevitably goes to court. “President-elect Donald Trump could rescind the order, but the 1953 statute Obama is invoking doesn’t include an explicit provision for reversal and that question could be tied up in court for years,” according to Bloomberg.

Just last year, the Obama administration gave the go-ahead to Royal Dutch Shell to drill into the ocean floor off the northwest coast of Alaska, making it the first drilling there in 20 years. Shell poured $7 billion into exploring the region, but came up empty and abandoned the project last year. According to the Washington Post, the new restrictions do not affect current leases held by oil and gas companies in the area. In March, the Obama administration reversed course on its plan to allow offshore drilling in the Atlantic from Virginia to Georgia.