Tests have shown that avian botulism caused the deaths of dozens of ducks in Fairmount Park in Riverside, city officials said this week.

Earlier this month, mild algal blooms were observed in the lakes at Riverside Park.

In mid-July, a pump failed, which “resulted in a lowering of the water levels in the lakes,” said Anthony Zamora, deputy director of the Riverside Parks Recreation Community Services Department, in a video call on Tuesday, August 13.

“Since then, it has been fully functional. The water level is where it needs to be and the water is circulating as intended,” Zamora said.

Botulism is caused by bacteria in the soil. According to the United States Geological Survey, high temperatures, too many plants and low oxygen levels in the water can lead to botulism. When birds feed on the vegetation, they can become sick – affecting the animal’s nervous system and sometimes leading to death.

According to the United States Geological Survey, outbreaks of botulism in birds generally pose a low health risk to humans.

Two autopsies were performed on ducks and avian botulism type C was detected.

No dead ducks have been found for almost three weeks, Zamora said.

The low water level and high temperatures created conditions for botulism in birds. The ducks may have fed on algal blooms or decaying plant material.

A similar outbreak at the lake in 2011 was thought to be caused by avian botulism.