In the animated movie “Finding Dory,” a blue fish with short-term memory swims thousands of miles from home in a quest to find her parents.

That’s admirable. But for the Wood Lake Nature Center in Richfield, invasive aquatic species like Dory — in this case, thousands of giant goldfish — are threatening to destroy its cattail marsh habitat.

“We want to kill Dory,” quipped Karen Shragg, the center’s director.

The nature center, located near Interstate 35W and W. 66th Street, recently was awarded a $5,500 grant from Hennepin County to help eradicate the goldfish population in Wood Lake. The money will be used to buy 150 largemouth bass to eat the goldfish, and also launch a campaign to teach people how to properly dispose of unwanted fish.

Goldfish will be the focus of the nature center’s annual benefit April 28. Peter Sorensen, a professor of fisheries and wildlife at the University of Minnesota, will speak on how to restore the lake’s natural balance.

Goldfish easily adapt to cold-water environments outside of tanks, Sorensen said. “They’re a real fish. They do really well in the right circumstances when they’re released into the wild,” he said.

Residents who want to get rid of pet goldfish often release them into shallow waters like Wood Lake, Shragg said. The goldfish then breed, thrive and grow in size, sometimes to a foot in length.

They do well particularly in degraded ponds that suffer from winterkill, when ice and snow reduce oxygen levels and kill weaker species.

Restoring biodiversity

Shragg first noticed goldfish five or six years ago at Richfield Lake, which is connected to Wood Lake by a stormwater pipe. The fish appeared in Wood Lake shortly after.

“The first couple of years ... we didn’t notice a lot of differences in the marsh,” she said. “But now it’s really very, very obvious how detrimental they’ve been.”

The goldfish multiplied and began to compete with native sunfish and minnows for food. They sucked food off the bottom of the lake, disrupting plant life and churning the water.

“The water used to be so clear,” she said. “They eat, they defecate, they eat, they defecate. ... It’s just unpleasant all the way around.”

Each spring, the nature center hosts a class that studies the biodiversity of the marsh.

“We were used to getting 15 different organisms,” she said. “Now we’re just happy to find one or two or three.”

Shragg said the problem of invasive goldfish has only gotten worse since last year.

Although it is illegal to release goldfish into public waters according to the state Department of Natural Resources, the center is not looking to prosecute lawbreakers, said Gordon Hanson, chair of the nature center’s board. Besides, he hasn’t caught anyone doing it.

Instead, he wants to tell people that unwanted goldfish can be donated to organizations like Minnesota Sea Grant and the Minnesota Aquarium Society. Even some pet stores will take them, Sorensen said.

Natural predators at the lake do eat the goldfish, including birds such as double-crested cormorants and great blue herons. But there are not enough to dramatically reduce the population.

The center plans to release the largemouth bass into the lake sometime this spring. “My guess will be that one round of this won’t do it all,” Shragg said.

Staffers will place posters and literature around the nature center warning of the danger of invasive species.

“My main point is to let people know how devastating something as innocent as goldfish can be,” Shragg said. “I don’t think people who are not ecologists or nature lovers understand the value of biodiversity.”