The federal government declared BP’s Macondo oil well dead on Sunday, nearly five months after it blew out of control, unleashing an environmental calamity in the Gulf of Mexico.

“We can finally announce that the Macondo 252 well is effectively dead,” Adm. Thad W. Allen, the retired Coast Guard officer who leads the federal spill response, said in a statement. The well, he said, “poses no continuing threat to the Gulf of Mexico.”

Crews aboard the Development Driller III rig conducted a pressure test early Sunday on cement that had been pumped into the bottom of the once-gushing well through a relief well. The test confirmed that the cement formed an effective, and final, seal to prevent oil and gas from coming up from a reservoir about 13,000 feet below the seabed.

In a statement, President Obama hailed the work as an “important milestone in our response to the BP oil spill.” He said the government remained committed “to doing everything possible to make sure the Gulf Coast recovers from this disaster.”