While rejecting TransCanada’s initial Keystone XL pipeline application to build the pipeline across the border from Canada, President Obama has embraced the southern leg of the project, which would ease a bottleneck that is slowing the movement of oil supplies from Canada and North Dakota to refineries on the coast of the Gulf of Mexico.

On March 22 in the Cushing, Okla., oil terminal and pipeline crossroads, Obama directed agencies “to cut through the red tape, break through the bureaucratic hurdles, and make this project a priority . . . and get it done.”

On Friday, TransCanada received the last of three permits it needed from the Army Corps of Engineers to begin construction on the 485-mile stretch of pipeline.

The permits dealt a blow to efforts by national environmental groups to slow the momentum behind the southern leg of the project — now also known as the Gulf Coast project. Those groups, including Friends of the Earth and the Sierra Club, have urged their Texas supporters to send comments to the Army Corps, which governs pipeline permits there. The groups have highlighted dangers linked to wetlands and rivers.

But the Army Corps have moved ahead. The Galveston branch on June 25 gave TransCanada the go-ahead for a stretch of the line, even though the agency said that the 36-inch pipeline would cross 654 “aquatic features.”

“Please let us know when you complete your project by returning the enclosed pre-addressed postcard,” the Galveston District regulatory branch chief Fred L. Anthamatten said in his letter to TransCanada’s Houston office.

The Galveston District said that TransCanada would use horizontal drilling to burrow under the water areas, but in some places would have to offset damage by buying credits from the Piney Woods Wetland Mitigation Bank, which was established by The Conservation Fund in 2008 to restore native hardwood forest.

On June 29, the Tulsa, Okla., branch of the Corps also issued a permit for the line and the Fort Worth district added its approval Friday.

Environmental groups have appealed to the Environmental Protection Agency to step in under the Clean Water Act and overrule the Army Corps.

Keystone is not the only project that environmentalists and their allies are seeking to block by appealing to the EPA. Activists are opposing permits for massive mineral extraction projects in the Rocky Mountains, Northwest coast and Alaska.

Under the Clean Water Act, EPA can veto any Corps-approved operations that would severely impair important waterways. The agency has invoked this power only 13 times.

In Alaska, a coalition of tribal leaders, fishing operators and environmentalists are fighting a proposed gold and copper mine, which could affect the Bristol Bay watershed. In May, the EPA found that a large-scale mining operation would harm fish habitat in the region, which boasts nearly half the world’s sockeye salmon.

Jason Metrokin, president of the Bristol Bay Native Corp., said that dozens of tribes in the area have urged EPA to scrutinize the Pebble Mine’s impact on their traditional way of life and a commercial fishery worth nearly $500 million a year.

“People in Bristol Bay have been living off salmon for 10,000 years,” Metrokin said. “It’s the social lifeblood of Bristol Bay. It’s a subsistence lifestyle.”

Northern Dynasty Minerals and its subsidiary, Pebble Limited Partnership, have not yet formally applied for federal and state permits. Company officials argue the EPA should hold off judging the project until the permits are under review.

Thousands of miles away others are trying to derail three proposed export terminals in the Pacific Northwest that would ship coal mined in the Powder River Basin to Asia.

K.C. Golden, policy director for the advocacy group Climate Solutions, said the EPA should step in if the Corps fails to weigh regional impact as well as the greenhouse gases that will be released once the exported coal is burned. “We need a thorough, comprehensive federally coordinated review of the full set of impacts,” Golden said.