NEWARK — Dead fish, nearly all carp, are floating to the surface at Lakeshore Park, and city officials wonder why.
They also question why so many carp, a freshwater fish native to Asia and Europe, ended up in the human-made lake in the first place.
Carp is an edible fish consumed around the world. It’s also popular as an ornamental fish that people keep in tanks and ponds. Koi is a subspecies.
But carp should not be in the water of Lakeshore Park because it’s considered an invasive species, according to Newark officials.
They are now reviewing city records to find out if someone, maybe years ago, added carp to the lake and their numbers grew. Or if people just decided to release live carp into the lake without notifying anyone.
“It’s speculation at this point,” said Soren Fajeau, Newark’s public works director, about how the fish arrived in the lake.
The 16-acre lake is a popular spot with fishers, joggers and those who enjoy hiking along its edge or watching birds settle on its surface or in the trees nearby.
Reports of dead fish drifting on the lake’s surface began Sept. 17. More reports arrived the next day, confusing city officials.
“We were not sure what was going on,” Fajeau said.
The number of dead carp at the lake is staggering: Up to 500, said Fajeau, noting the number was tallied after workers began scooping them from the water and shoreline.
“We do not know how such a high number of carp got into the lake,” he said during an interview. “It’s a freshwater lake. They are not native, and they do not belong there.”
Patrick Foy, a spokesman for the California Department of Fish & Wildlife, was not surprised that dead fish might be appearing at the East Bay park at this time of year.
“It’s widely believed to be the result of dissolved oxygen in the water,” Foy said about the cause of carp deaths. “That can be a result of high (weather) temperatures, which we have had recently and which often happens in late summer.”
According to The Noble Research Institute, a nonprofit agricultural research organization based in Oklahoma, warm water has lower oxygen levels than cold water.
Also, water plants grow more during the summer than the rest of the year, and while during the day the plants put oxygen into the water, at night the plants take up oxygen, creating a high demand for it among plants and wildlife.
If the plants and fish use more oxygen during the night than is available, a fish kill might occur, according to the institute’s website.
“You can also have an algae bloom,” said Foy, who suspects that is what happened in Newark. “All these factors combined together will kill the fish.”
California is undergoing a drought, and rainwater that would traditionally replenish the freshwater lake in Newark is not happening, meaning there’s less water supply to keep oxygen levels high.
Still, seeing dead fish drifting around the lake has disturbed some visitors.
“There are big fish and small little fish and they are all dead, all spread throughout (the lake),” visitor Cassandra Trejo told KTVU Fox-Two.
Tejo added that other fish are “gasping for air” at the park.
Newark workers have installed machines around the lake to boost oxygen levels, Fajeau said. They also have pumped water into the lake from fire hydrants to increase water levels.
The idea is to stop the fish kill.
Along with carp, there’s trout and bass in the Newark lake, Fajeau said. Mostly, the other species were not affected by the drop in oxygen levels. The reason is not clear.The city plans to create a website to keep people updated on what’s happening at Lakeshore Park, including with the fish, Fajeau said.
“It’s definitely stabilized right now,” he said about the loss of fish. “But we are doing all we can to address what’s happening.”
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