On Sunday, environmental officials in Jalisco, a state in western Mexico, declared an emergency amid the mysterious deaths of fish living in the Cajititlán lake.

According to EFE, the deaths were noticed last week, and officials began an investigation on Sunday. That same day, officials reported removing more than 53 metric tons of decaying the fish corpses -- of a finger-sized chub species -- from the lake by use of a bulldozer, boats, shovels and wheel barrels, The Associated Press reports. Those removing the fish wore masks to protect themselves from the rotten smell.

"It's more [than the city government says]," Octavio Cortes, Cajititlán fishing cooperative president, told EFE. "Just last Tuesday, we filled nine trucks, one a seven-ton [truck] and the other a four-ton [truck]. This is critical."

The fish bodies are being tested, but a cause for the die-off has yet to be determined. AP reports the Jalisco state environment department said the cause is not natural.

Manuel Guzman Arroya, director of the University of Guadalajara's Fresh Water Institute, disagrees. He argues that winds could have whipped up sediment in the shallow lake and suffocated the fish by preventing them from getting oxygen.

"The lake has problems because too much water is being drawn off, and its level is very low," he said.

Cajititlán lake is used to provide irrigation and recreation for housing developments in the surrounding area, but Arroya said that pollution was not a big cause of the fish die-off.

This marks the fourth fish die-off in the lake this year.

On Monday, authorities also announced that an Aug. 27 fuel spill caused the death of dozens of various fish, birds and turtles living in a river in the state of Veracruz, located on Mexico's Gulf Coast. The oil spill spread for about 0.75 miles (1.2 kilometers) and was caused by a group illegally siphoning gas from a pipeline.

Dalos Rodriguez Vargas, the Veracruz state environmental prosecutor, said officials are now concerned about heavy rain spreading the fuel to an adjacent lake.

"The danger is that if it rains more, with the tropical weather system out there, it could overflow again if they don't get it gathered up quickly and reach the lake," he explained.

"They are working with all possible speed to get it contained."

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Follow Scharon Harding on Twitter: @ScharHar.

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