They lurk in our lakes and streams

Carp that jump over boats, snails that infect ducks with killer flukes, docks crusted with zebra mussels, suburban lakes that are juiced up with lawn fertilizer and matted with Eurasian milfoil and now — Carassius Auratus … goldfish.

Goldfish? Yes, goldfish.

The lakes and ponds that provide Eden Prairie and neighboring communities with jewel-like appeal are under attack by finny pets intended for fish bowls.

Goldfish now have ranking on the Minnesota Aquatic Invasive Research Center’s priority list for investigation.

Of recent local note:

July/August 2020, Edina — Solar-powered antennas track Lake Cornelia carp and goldfish.

Oct. 26, 2020, Chaska — From 30,000 to 50,000 goldfish removed from Big Woods Lake inlet.

March 30, 2021, Eden Prairie — 196 goldfish harvested from a pond near Staring Lake.

July 2021, Burnsville — Goldfish the size of an official NFL football taken from Keller Lake.

Should we be worried?

We asked the experts if Eden Prairie needed to worry.

City Water Resources Coordinator Leslie Stovring answered in the affirmative: “We take these tiny, cute little fish, and we throw them in a lake, and they explode in size.” Goldfish are invasive bottom feeders that harm water quality and threaten ecological health.

Stovring noted that the large stormwater pond near Staring Lake Nature Center and Duck Lake near Prairie View School were full of wild (or feral) goldfish. She added that they can be hard to spot from shore or in waters with algae blooms or dense aquatic vegetation.

That proved to be true in April and October when this reporter intended to photograph the orange menace in both shallow bodies of water. Pictures were snapped of what everyone sees on a windless day in Eden Prairie — Mother Nature in her prime — but no bottom feeders.

This week, searches of the DNR’s 2021 fishery inventories and the websites of local lake associations revealed no listings or references to goldfish in Mitchell, Red Rock, Staring, Riley, Bryant and Round lakes.

It is understandable why the goldfish threat has yet to claim chat time in local coffee shops and Rotary Club meet-ups. Goldfish fascinate children and, perhaps, serve as therapy pets for the rest of us. Eden Prairie’s lakes and ponds are perceived as comfortable and convenient options for families wanting a kid-sensitive way to bid farewell to pet fish that have been sharing a pre-teen’s bedroom.

“Basically, people are trying to set them free,” says Stovring, “and that is not a good thing for our lakes.”

Like bottom-feeding carp, goldfish stir-up lake beds and uproot plants. The resultant turbid water screens out sunlight, reducing the amount of oxygen produced by aquatic plants. Sunfish, crappies, bass and northern pikes need oxygenated waters. Goldfish, not so much. If left uncontrolled, carp and goldfish can unbalance a lake’s native ecosystem.

Tougher than we thought

Goldfish are closely related to crucian carp. Carassius carassius live in the northerly latitudes of Europe. They have adapted to very harsh conditions. A scientific study of them in Europe suggests that 8-million years ago, the common ancestor of each evolved a special trait passed on to “modern” goldfish and crucian carp: they can live without oxygen in cold, frozen lakes for up to five months. Sunfish and perch can not. Come spring, with fewer predators, goldfish and carp spawn and multiply.

And not being confined to a fishbowl with only fish flakes to nibble as they lazily circle ornamental mermaids, Little Nemo and Bubbles get really big. That’s what the City of Burnsville and a carp control contractor learned in July on Keller Lake. They hauled in goldfish measuring up to 18 inches and 4 pounds.

Two and a half years ago, Carver County Water Management (CCWM) spotted a large school of goldfish in an inlet to Big Woods Lake, one of a chain of five lakes in Chaska.

CCWM staff responded. They tagged and tracked 500 goldfish to discover their movements and their spawning, nursing and wintering areas. They also tested several goldfish removal techniques.

Project videos show thousands of orange, brown and pale goldfish silently moving through still water — their dorsal and tail fins gently rippling a glassy surface.

In October 2020, the project removed between 30,000 and 50,000 goldfish from the Big Woods Lake inlet, a channel connection with Lake Hazeltine. The Carver County Water Management website notes that the large haul had only removed a portion of the invaders.

Watershed District concerns

Terry Jeffrey anticipates that the Riley Purgatory Bluff Creek Watershed District (RPBCWD) will begin targeting feral goldfish within its jurisdiction (which includes much of Eden Prairie) after taking measure of the Carver County programs and DNR advisories.

Jeffrey, the district’s interim administrator, said there is growing concern. His agency netted 136 goldfish in March from a large stormwater retention pond near Staring Lake Nature Center that edges up to an Oak Point School parking lot. He added that district staff is well aware of Duck Lake’s invaders.

Stovring told EPLN that when the levels of Duck Lake and the pond near Staring Lake Nature Center rise too high, their respective overflow pipes empty water into Purgatory Creek. The pipes can serve, it seems, as Valleyfair-like water slides for goldfish. Once in the stream, they can migrate onto Staring and Purgatory Creek Park lakes and the Minnesota River.

Nine Mile Creek Watershed District administrator Randy Anhorn says that fishery inventory checks have not found goldfish in Smetana Lake. The same holds true for Bryant Lake. But, the Eden Prairie-based agency has partnered with the City of Edina on a study of Lake Cornelia goldfish.

The study involved capturing and tagging goldfish and tracking them with solar-powered, triangulated antennas in Lake Cornelia and associated lagoons.

The Lake Riley carp project

A globally significant and pioneering University of Minnesota study of common carp that began in 2006 on Lake Riley is making a difference.

Headed by Fisheries, Wildlife and Conservation Biology professors Peter Sorenson and Przemek Bajer, the study examined carp life, habits and seasonal movements in the chain of lakes formed by Riley, Rice Marsh, Susan, Ann and Lucy lakes. The project also tested and fine-tuned carp research protocols and management and removal techniques.

The knowledge gained in Chanhassen and EP waters has been adapted for carp and goldfish projects elsewhere. Environmental agencies, scientists and activists agree that we need to know what’s actually happening in the turbid shallows that dot the metro region.

This just in: EPLN has learned that experts are examining what they suspect is a new carp/goldfish hybrid that was recently discovered at Normandale Lake in West Bloomington. That’s something to think about.

So where can Bubbles and Little Nemo go?

Consider how unexpectedly tough and aggressive your mild-mannered goldfish become when given a lake home.

And consider one of the Minnesota Aquarium Society (MAS) “surrender events.” Surrender events for goldfish are sometimes run during the society’s bi-monthly auctions of tropical and marine fish and plants.

MAS aquarist Randy Carey advises folks to check the MAS website for surrender event dates. MAS volunteers also help coordinate goldfish “re-homing” events through their website’s “Contact Us” form.

Fun fish facts

Fun fish fact 1: University of Norway researchers say that crucian carp and goldfish can metabolize carbohydrates into alcohol in a process that enables them to survive long, cold and sunless winters. At times, the alcohol levels in the two fish exceed the legal blood alcohol limits set for car drivers.

Fun fish fact 2:  When they were kids, environmental administrators Leslie Stovring, Terry Jeffrey and Randy Anhorn never kept pet goldfish.

Fun fish fact 3:  When writer Jeff Strate was a kid adventuring in and around Lake Cornelia, he never released his goldfish, guppies and angelfish to the lake or Shaughnessy Pond.

Contributing writer Jeff Strate serves on the Board of Directors of the Eden Local Prairie News.