Faecal bacteria are contaminating water in wells and sinkholes in Mexico’s Yucatan state, which are a vital source of drinking water, according to a report by Greenpeace, a global environmental organisation.

The report, published on Tuesday, said nearby pig farms and municipal wastewater were likely sources of the pollution in the southeastern coastal state.

“A range of chemical and microbiological indicators reveal a complex mosaic of severe, localised organic pollution,” it said.

Greenpeace called for an immediate moratorium on new industrial livestock operations and farm expansions in the peninsular state, which was once home to the ancient Maya civilisation.

With no above-ground rivers, groundwater is the Yucatan’s only freshwater source, and the area’s porous limestone bedrock lets pollutants quickly seep into the aquifer.

The global environmental watchdog group commissioned an independent laboratory to test water at 17 sites near the state capital, Merida, in August.

The sites included household and farm wells, community water points and cenotes, the natural sinkholes that dot the Yucatan Peninsula, which is one of Mexico’s most popular tourist destinations.

According to the report, every sample showed some degree of contamination likely linked to faecal waste, and several sites appeared heavily polluted. Total coliform bacteria reached the test’s upper limit in 16 of 17 samples, and faecal coliforms did so in 13.

However, the tests cannot show whether the waste came from people or animals, and leaking septic tanks and municipal sewage may also contribute to contamination.

Greenpeace said, however, that separate testing using Pig2Bac, a pig-specific DNA marker method, detected pig faecal matter in samples analysed at laboratories at Johns Hopkins University in the US and Mexico’s National Autonomous University (UNAM).

Greenpeace said the results raise “critical accountability questions” about nearby pig farms. Maya communities joined Greenpeace in demanding action from environmental authorities over the contamination.

A UN report published in July found that there are more than 500 industrial pig farms across Yucatan state with more than 50,000 animals, many located near the lands and territories of Indigenous Peoples.

Marcos Orellana, a former UN special rapporteur who authored the report, said waste and chemicals from industrial farms “find their way very quickly” into the water communities use for bathing, cooking and drinking. He said most farms lack required permits and that regional government initiatives “remain insufficient”.

“The contamination of the waters that have sustained Mayan culture for millennia is predominantly coming from the industrial operations of the growth of animals,” Orellana said.

But Antonio Zumarraga, vice president of the Yucatan Citizen Scientific Water Observatory, defended the local pork industry, saying the sector has invested in water treatment and supports conservation programmes. He blamed local authorities for their inaction.

“It’s an issue that, as long as it doesn’t carry political weight for the government, they won’t do anything about it,” Zumarraga said.

The Yucatan state government was not available for comment, while Mexico’s national water commission, CONAGUA, did not immediately respond to a request for comment. Merida’s Association of Pig Farmers also did not respond to a Reuters request for comment.