EL ROSARIO, Mexico - Surrounded by the millions of monarch butterflies that Mexican environmental activist Homero Gomez fought to protect until his mysterious death, relatives and friends paid tribute to him on Thursday.

Gomez's sudden disappearance two weeks ago had sparked an outcry in Mexico, an increasingly violent country where activists are routinely threatened, harmed or even killed as a result of their work.

The attorney general in the western state of Michoacan confirmed on Wednesday only that Gomez had drowned; the exact circumstances of his death remain unclear.

Relatives and friends carried his coffin, covered in a Mexican flag and adorned with flowers, to the entrance of the El Rosario reserve, before moving through the streets of the village nearby and finally his home.

Gomez had spent a decade working as an activist, though he became best known for posting mesmerizing videos of the black and orange insects on social media, urging Mexicans to treasure the El Rosario reserve, a world heritage side.

Amado Gomez said his brother, an engineer, was so compelled to do something after the number of butterflies dropped dramatically that he eventually gave up his job to work on different projects aimed at protecting them.

"This was his passion," said Gomez. "He loved promoting the butterflies, filming them, researching them."

In recent years, he had increasingly pushed for reforestation projects to save their habitat.

Gomez said his brother affectionately called them "girlfriends of the sun".

Millions of the butterflies make a 2,000-mile (3,220-km) journey each year from Canada to winter in central Mexico's warmer weather. However, they are facing new challenges linked to extreme weather and changing habitat.