WASHINGTON — As many as 50 manatees have died in Mexico, floating to the surface of rivers and lagoons in the southern state of Tabasco, where some of the country’s major oil wells have been operating for decades. Fish, reptiles, birds, and other marine animals have also died suddenly, and scientists are scrambling to figure out the cause.

‘‘It could be one of the greatest environmental emergencies we have had in recent times,’’ Ernesto Zazueta, president of the Association of Zoos, Breeders, and Aquariums of Mexico, told the El Universal newspaper.

On May 18, residents of the municipality of Bitzales found a lifeless manatee floating in the water. In the weeks the followed, more dead manatees were found in the state’s waterways. The government of Tabasco has identified 29, but residents say the number is closer to 50.

Fishermen reported that suddenly they weren’t catching anything, and dead fish also began floating to the surface.

Officials have sampled the water and carried out necropsies on the animals, but the cause of the die-off remains a mystery.

One study found high levels of lead and cadmium in the water. But other biologists said toxic substances have not been found in their tests of the water and the manatees.

washington post