Petroleos Mexicanos, known as Pemex, said in a statement that its crews had reacted “immediately” to stop and contain the spill around the town of Alamo, one of the communities hit hardest by the recent flooding.

The company did not say when the spill occurred or exactly what spilled.

But Alamo resident Arturo de Luna said locals became aware of it over the weekend. “Sincerely, we’re very worried,” he said.

At least 76 people died in heavy rains from Oct. 6 to 11 across several states in central and eastern Mexico. Some three dozen remain missing and more than 100 communities remain inaccessible by road.

Alamo, along with Poza Rica, were the most affected communities in northern Veracruz state. Residents in part of Poza Rica found their homes’ walls streaked with oil after waters from the Cazones River receded, though no spill was confirmed there.

The Pantepec River crosses northern Veracruz and supplies water for a number of communities, including the city of Tuxpan near where the river dumps into the Gulf of Mexico.

Tuxpan Mayor Jesús Fomperoza said on Facebook on Tuesday that Pemex, the navy, security forces and energy and environmental agency personnel were working with local and state officials to keep the spill from reaching municipal water systems.

He said private businesses, fishermen and others had helped to install containment barriers.

But the spill was affecting lives along the river.

De Luna, the Alamo resident, said boat services that locals use to move across and up and down the river were suspended, cutting off some river communities.

Alejandra Jiménez, an activist with Foundation Chalchi, a nongovernmental organization focused on protecting water resources, said it was too early to determine the spill’s environmental impact but that recovery of the ecosystem could take years.

“The prevention phase didn’t happen, so now they have to keep it from spreading,” she said.