A raging fire on the surface of the Gulf of Mexico near a Pemex offshore oil platform last Friday provoked a Twitter storm. But officials in Mexico say it wasn’t the environmental disaster it appeared to be.

On July 3, a video posted on social media from a nearby helicopter showed three ships trying to douse flames emerging from the sea. The shocking footage sparked criticism internationally on social media, including from famed environmental activist Greta Thunberg and U.S. Senator Bernie Sanders.

But Mexico’s President Andres Manuel Lopez Obrador and Pemex executives were quick to point out that the fire wasn’t caused by an oil spill. A marine pipeline connecting to platforms that make up the Ku-Maloob-Zaap cluster of fields leaked nitrogen gas, which was ignited by an electrical storm.

Petroleos Mexicanos, as the state oil company is more formally known, said in a statement that no environmental damage was caused by the leak that began at 5:15 a.m. local time and operations had returned to normal five and a half hours later. Pemex said interconnection valves in the pipeline were closed to control the gas leak and nitrogen was injected into the busted pipeline.

Pemex said it will investigate the cause of leak. Meanwhile, some environmentalist groups remain unconvinced by the company’s assurances, and are calling for a detailed study of the fire’s environmental impact.

Greenpeace Mexico executive director Gustavo Ampugnani issued a statement shortly after the news of the fire, decrying the environmental and safety risks posed by “the fossil fuel extractivist model” in Mexico. “It will be necessary to see how big the impact was on the surrounding marine ecosystem,” he said.