Homero Gomez Gonzalez, 55, had been missing since January 13, police told CNN Espanol. He was found in Ocampo, Michoacán state, Mexico President Andres Manuel Lopez Obrador said at a Thursday press conference.

Homero Gomez

Lopez Obrador called Gomez’s death “lamentable and painful” and vowed to continue to fight criminal groups believed to be behind his disappearance and death.

According to the Michoacan prosecutor’s office, Gomez’s body was found with a head injury and he died of drowning. His body was found in a retention pond. An earlier report indicated it was in a well.

An official autopsy will be released at a later date.

Mexico’s State Commission for Human Rights said they believe Gomez, known as the “Defender of the Monarch Butterfly,” might have come into conflict with illegal loggers while carrying out his conservation work.

People carry the coffin with the remains of Mexican environmentalist Homero Gomez, during his funeral procession in El Rosario village.

“The latest survey of monarch butterfly habitat in Mexico is a testament to the power of conservation. The area of forest occupied by hibernating monarch butterflies in Mexico has increased by 144% in relation to last year’s survey — the biggest growth in the past 12 years,” the World Wildlife Fund reported.

Gomez would post videos of himself with the thousands of Monarch butterflies in the sanctuary he created, El Rosario Sanctuary in Ocampo.

“Today, the butterflies are flying around looking for water as they do nearly every day before they head home,” Gomez said the day before he disappeared.

This article has been updated to add detail about how Homero Gomez Gonzalez died and where his body was found; the update also removes a reference to the endangered status of the butterflies.