Thousands of fish have died from an unknown cause in a canal in Tampico, Tamaulipas.

The city’s Canal de la Cortadura, a popular tourist area, was clogged on Tuesday with a massive die-off of catfish. As of Wednesday, a total of 12 tonnes of dead fish had been pulled from the canal.

There was speculation that the deaths could have been due to a chemical product that was dumped into the Pánuco river, which runs through the coastal city, or a lack of oxygen caused by high temperatures.

“What’s begun happening in the canal is very dangerous, because it’s home to many species, not just catfish,” said local business owner Carmen González Navarro.

“It means that everything living in the canal could be dying, which is why we’re hoping the municipal secretary of ecology will tell us what’s happening,” she said.

González said that on Tuesday morning “we began seeing a huge quantity of little fish floating on the surface of the canal, and some were still alive. The color of the water began to change to a thick green” but no one is saying why.

Tampico officials have been cleaning the canal since the dead fish began accumulating. They pulled five tonnes out on Tuesday, and other seven today.

“This morning we woke to find many more dead fish, and now we’re getting close to, I believe, 12 tonnes,” said spokesman José Shekaivan Ongay. “Cleaning squads are working to remove them and avoid an unhealthy situation.”

Ecology Secretary Alejandro Deutsch Lozano claimed that the die-off was due to a lack of oxygen in the water caused by high temperatures.

Specimens were taken for analysis to determine the cause of death.

“We also believe it could have been due to the salinity of the water,” said Deutsch.

Sources: El Sol de Tampico (sp), Milenio (sp), Milenio (sp)