Faecal bacteria are contaminating vital drinking water sources in Mexico’s Yucatan state, according to a report released Tuesday by the environmental organization Greenpeace. The pollution affects wells and natural sinkholes, known as cenotes, which are the region's sole source of freshwater.

The report suggests that nearby industrial pig farms or municipal wastewater systems are the likely culprits behind the contamination in the southeastern coastal state. The Yucatan Peninsula's porous limestone bedrock allows pollutants to seep rapidly into the groundwater, making the issue particularly concerning.

Greenpeace commissioned an independent laboratory to test water samples from 17 locations near the state capital, Merida, in August. These sites included wells, community water points, and cenotes. Laboratory results indicated that every sample showed some level of contamination, with several sites appearing heavily polluted. Total coliform bacteria exceeded the test's upper limit in 16 out of 17 samples, and faecal coliforms reached the limit in 13 samples.

The findings raise significant concerns about the safety of the water supply for residents and the region's popular tourism industry. Greenpeace is calling for an immediate halt to new industrial livestock operations and farm expansions in the state.

While the initial tests could not distinguish between human and animal waste, further analysis using a pig-specific DNA marker method, Pig2Bac, detected pig faecal matter in samples. These tests were conducted at laboratories at Johns Hopkins University in the United States and Mexico's National Autonomous University (UNAM), according to the report.

These results prompt "critical accountability questions" regarding the impact of nearby pig farms on the local water quality. Indigenous Maya communities have joined Greenpeace in urging environmental authorities to address the contamination.

A United Nations report from July highlighted the prevalence of industrial pig farming in Yucatan, noting over 500 such farms housing more than 50,000 animals, many situated near Indigenous territories. The former UN special rapporteur who authored that report stated that waste and chemicals from these farms "find their way very quickly" into water used for daily life, and that most farms operate without required permits, with government initiatives deemed "insufficient."

Given the Yucatan's lack of above-ground rivers, its groundwater is the only accessible freshwater. The extensive network of cenotes, often used for recreation and as water sources, are particularly vulnerable to contamination from the overlying land.