Goldfish infestation costs Wilmington $320,000

• The restoration project is budgeted at $320,000.
• Public Works responded after neighbors alerted them about the fish population.
• The fish were multiplying and overwhelming the park's ecosystem, a city official said.

The city of Wilmington is spending over $300,000 to restore a pond that was overrun by up to 600 pounds of goldfish.

"It was an orange mass of fish," said Sean Duffy, the water division director for the Public Works Department.

The fish, Asian carp commonly owned as pets, were 4 to 6 inches long each, Duffy estimated. Feeding time was a sight to see, said Sally O'Byrne, who lives across the street from the pond at Cool Spring Park.

"When the guys would throw bread in, there would be a golden mound that would rise up out of the water," she said.

The city started work about three weeks ago to drain the water and remove the fish and overgrown plants from the pond, which is over an acre in area and up to 10 feet deep, Duffy said. It is different from Cool Spring reservoir, which sits underground at the park, but not directly under the pond.

The fish, an invasive species, had to go because without a predator, they overwhelm the ecosystem.

"You start losing diversity," Duffy said.

Carp are "fast-growing, aggressive and adaptable" fish that are invading waters throughout the United States and hogging resources from native species, according to the National Wildlife Federation.

Cool Spring Park used to have 13 species of dragonflies and damselflies, said O'Byrne, who has a master's degree in environmental planning and assisted in the park's design. Now, she said those creatures are rare.

Alison C. Etinoff, the contractor managing the restoration project, said some of the fish removed were as small as an inch long and some weighed as much as a pound. With swimmers of different sizes, she said it’s impossible to know how many there were.

“We lost count,” she said.

Duffy said “approximately 500 to 600 pound of goldfish were removed (about 4,000 fish).”

Duffy said all they can do is hypothesize about what caused the infestation.

"Some people may think, ‘There's no fish in here. Why don't we put them in there and make it more attractive?'" Duffy said. "And some people have fish they just don't want and don't want to kill them. They figure there’s a big body of water. Why not put them in there?"

The city learned of the problem over a year ago when neighbors complained, Duffy said.

"When we saw the number of fish, and they were just multiplying, we realized we were heading toward a catastrophe," he said.

O'Byrne said the waste produced by the fish acted as a fertilizer for the cattails at the edge of the pond.

"They were growing so tall that you couldn’t even get a view of the pond from the areas around it," Duffy said.

Clara Zahradnik, who lives nearby, said the swarm of fish attracted fowl like a blue heron and a snowy egret.

"It would be this yellow-orange swirl. It was quite spectacular," she said. "They weren’t gobbling up the fish fast enough."

The $320,000 budgeted to restore the pond was taken from the water and sewer budget for fiscal year 2017, Duffy said. It will cover the cost of draining and refilling the pond, replanting native plants and stocking the pond with native fish, such as bluegill and largemouth bass, which will "prevent a population explosion of goldfish if they were ever introduced again," Duffy said.

The park is slated to reopen by May.

"So much money was spent because mistakes were made," O'Byrne said.

The park area was previously an open reservoir dating back to the 1870s. The most recent incarnation of the park was opened to the public in 2009, Duffy said.

O'Byrne commended the park's design but said there were problems with ongoing care.

"It incorporated native plants that would be good for amphibians and dragonflies," she said. "But the maintenance crew was weeding it out. They didn’t recognize the plants. ... It was a problem of supervision and training."

The outcome for the removed fish appears grim.

The fish have been "rehomed," Duffy said, but he doesn't know where all of them went.

"Some went to places they could continue to live and thrive," he said, but added, "I don't believe the entire population ended up finding new homes."

Though initially the plan was to donate some of the fish to the Tri-State Bird Rescue & Research, Duffy said “the facility could not receive them due to full capacity, so the fish were repurposed.”

Duffy said the experience has been an educational one for his Public Works Department.

"What we’ve learned is there’s a certain amount of ongoing maintenance (required)," he said. "We'll probably have it in our new plan, but when we built the pond, we weren’t anticipating some of these issues."

O'Byrne said the situation is a lesson for residents, too.

"If the person who first put those first three fish in the lake, if he’d gotten rid of them in a humane way, none of this would’ve happened," she said. "Somehow people value their pets over other wildlife."

Contact Christina Jedra at cjedra@delawareonline.com, (302) 324-2837 or on Twitter @ChristinaJedra.