A pesticide is being applied at Leinweber to eradicate the goldfish population. (Photo Courtesy City of Medicine Hat)

By Chris Brown

Invasive Species

City taking steps to eradicate goldfish in Leinweber Pond

Aug 31, 2022 | 3:54 PM

MEDICINE HAT, AB – A tiny fish is causing a big problem at the city’s Leinweber Pond.

Goldfish are a fun pet to keep in your aquarium or pond but when people let them go in natural ponds they’re actually introducing an invasive species to the water.

Dave Genio, manager of parks with the City of Medicine Hat, says the problem is goldfish can have many babies during a season and with no natural predators they can very quickly take over habitats.

Their effect on the ecology of the area can be so dramatic that plant and insect species aren’t able to survive. In the case of Leinweber Pond, one concern is the depletion of the leopard frog habitat

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“We looked at various different solutions so you know biological solutions, mechanical solutions and as well chemical solutions,” Genio says. “And working with Alberta Environment and Park and information provided through our contractor as well as investigating the best process, utilization of the chemical Rotenone was the best alternative in terms of full eradication or the best opportunity for full eradication of the invasive species in the pond.”

Genio adds nearby people may detect a bit of an order from the chemical but there is no adverse effect to humans or other animals.

He’s hopeful they only have to do this once but a second pesticide application may be needed in the next few weeks. Applying the pesticide is costing the city about $40,000.

Genio says the problem was created by people placing goldfish in the pond, and it’s unfortunate the city has had to take this step. He says current weighings of the biomass they’ve pulled from the pond is 250 pounds.

“It may not sound like a lot but we’re talking about really small fish that don’t weigh a heck of a lot. So it is staggering for the size of pond that we have and the amount of fish that unfortunately we’ve had to remove,” he says. “But we have to look at everything from all parameters what’s best for us being stewards of our parks and water bodies, what’s the best solution for this to hopefully take care of the issue and go from there.”

Genio says the city has received and is investigating reports of other goldfish in other bodies of water. He adds potential penalties for introducing an invasive species to a body of water include jail time and a large fine. If you can’t care for a fish in your aquarium or pond, the province suggests contacting a retailer or pet store, giving it to an aquarium or pond owner, donating to a school or talking to a veterinarian.

More information about the chemical being used is available on the Government of Alberta website.