Health authorities in Yucatán have closed six artificial lakes in Mérida after testing detected the amoeba Naegleria, including the dangerous species Naegleria fowleri, according to the Yucatán Health Ministry.

The closures followed the death in September of a 34-year-old water sports instructor who contracted a rare brain infection after working on the water at an artificial lake in the Plaza La Isla area.

Barriers and warning signs have been installed, and a minimum distance of three meters from the water's edge is required at lakes that tested positive, according to the Yucatán State Health Service.

The citywide testing drive examined nine urban water features in Mérida, and Naegleria microorganisms were detected in six of them. Yucatán's Health Minister Alberto Alcocer confirmed the findings.

Sites testing positive include the artificial lakes at La Isla, Cabo Norte, Parque Ecológico de Oriente, El Centenario Zoo and La Plancha, according to Yucatán Magazine. The remaining three tested negative.

Operators are beginning chemical sanitation protocols under technical guidance from specialists at the Autonomous University of Yucatán and the Center for Research and Advanced Studies, and the lakes will stay cordoned off until follow-up testing verifies safety standards are met.

Naegleria fowleri infections are extremely rare but almost always fatal, which is what gives this outbreak its public-health urgency. The organism thrives in warm freshwater, particularly in subtropical and tropical regions, according to the Robert Koch Institute as cited in the blue News report.

It can enter the brain through the nose while a person swims, causing primary amoebic encephalitis and meningitis that in most cases leads to coma and death.

Health officials note the amoeba is not transmitted person to person and cannot be contracted through casual contact, splashes, or drinking tap water.

Yucatán is a popular vacation destination, drawing international tourists to the Mayan ruins of Chichén Itzá and the freshwater cenotes, and the closures touch some of the metropolitan area's most heavily visited public and private spaces.

Authorities stress there is no general closure of natural swimming areas, and the affected lakes were ornamental features not approved for swimming or bathing.

At sites like Animaya, boat tours continue because visitors have no direct contact with the water, and all surrounding parks and zoological grounds remain open to families.

Medical surveillance teams monitored hundreds of people who had potential exposure in the weeks after the instructor's death.

The Yucatán State Health Service reports that 361 people who had contact with the lake water completed their monitoring period on October 4 without any further illness being recorded, indicating no other human cases have occurred.

Despite the official reassurances, Yucatán Magazine reports that social media users have spread conspiracy theories and exaggerated claims about the risk, which health officials reject as unfounded.

Restricted lakes will remain closed until chemical treatment is complete and follow-up testing confirms they meet safety requirements.

Yucatán's health service says it will continue inspecting artificial lakes across the state, and Mexico's Ministry of Health is planning a comprehensive review of all artificial lakes at risk of Naegleria fowleri contamination, particularly those within amusement parks.

Authorities advise people not to swim or immerse themselves in waters of unverified quality, and to seek immediate medical attention if symptoms such as fever, severe headache, nausea, vomiting or stiff neck appear after contact with suspected contaminated water.