NEW ORLEANS — A federal appeals court has revived an environmental group’s lawsuit to make BP PLC list the amount and type of every pollutant that got into the Gulf of Mexico during the 2010 oil leak.

But it upheld a judge’s decision that the rest of the Center for Biological Diversity’s lawsuit became legally irrelevant when BP capped the well.

The leak began in April 2010 after an explosion aboard the rig Deepwater Horizon, which had been leased by BP and had been working at the company’s Macondo well site about 50 miles southeast of the Louisiana coast. The rig sank two days later.

At estimated 200 million gallons of crude oil flowed out of the well before it was capped in July. The oil fouled coastal marshes and beaches and caused seafood harvest grounds to be closed periodically.

The 5th U.S. Circuit Court of Appeals’ three-judge panel took issue with BP’s contention that the pollution information was already readily available on the Internet, satisfying the Emergency Planning and Community Right-to-Know Act.

“Some of the Web pages cited in the defendants’ briefs lead to links to documents comprising thousands of pages of information,” Judge Carolyn Dineen King wrote in a footnote to the opinion joined by Chief Judge Carl E. Stewart and Judge Priscella R. Owen. “We do not think that the intent of EPCRA is met by requiring the public to search for a needle in a cyberspace haystack.”

BP had no comment on the opinion, which was filed Wednesday.

“It’s great that BP could be forced to disclose the amounts and toxic components of everything that spilled into the Gulf of Mexico. This public disclosure is important for the restoration of the area and for public health,” Miyoko Sakashita, oceans director for the center, wrote in an email Wednesday.

“While the decision on the public disclosure of the spill is a victory, we’re disappointed that the Clean Water Act claims have been dismissed,” she continued. “The lessons from the BP spill seem far from over, and there have been recent questions about discharges and oil sheens near the site. So we are considering our options for the dismissed claims.”

Officials have said that underwater inspections at the site of BP’s Deepwater Horizon rig disaster have failed to identify the source of a persistent sheen on the surface of the Gulf of Mexico — but the well and relief wells drilled to stop the gusher are secure. Lab tests were planned on a white cloudy substance, not believed to be oil, that appears to be coming from several areas on the overturned rig, officials said in mid-December.

The District Court ruled correctly that there were no continuing claims under the Clean Water Act and the Comprehensive Environmental Response, Compensation, and Liability Act because the well had been killed under federal orders and supervision, the 5th Circuit ruled.

“By all accounts in the record before us, the well site is now effectively dead. This is not the typical case where defendants may claim repentance and reform through voluntary action only to revert to their old ways upon dismissal of the suit,” King wrote.