The Bow River, famous for its trout fishing, has been inundated with a number of unwanted fish and anglers believe the invasive species have been intentionally introduced to the waterway.

“There are a variety of different fish that are purchased through the pet trade that are released into the rivers and Prussian carp is one of the most common ones being found in (southern Alberta’s) rivers now,” explains Brian Meagher, Trout Unlimited Canada’s Alberta Biologist.

Prussian carp and goldfish, which look similar and have nearly identical genetic makeup, have been located in the Bow River and in rivers throughout southern Alberta.

“In the Rosebud River, further north from us, the Prussian carp have taken over the system,” said Meagher. “They’re very small, they stunt, they stay very small and they’re very good feeders and they have a different lifestyle than the native fish.”

Prussian carp are voracious plant eaters and their waste depletes the oxygen supply in a waterway. Invasive species often thrive in new environments where natural control mechanisms are unable to regulate their numbers. Native species often suffer as a result of depleted resources.

According to Trout Unlimited Canada, the majority of the unwelcome species in Alberta’s rivers are the result of pet owners releasing the fish into the river after draining backyard ponds before winter’s arrival.

“They don't want their pet to perish so they take it down into the river and release it thinking it is just going to go away and it's isn’t a problem. The reality is (the fish) can be a problem.”

The Alberta Fisheries Act prohibits the release, or contributing to the escape, of fish into waters they did not originally come from. Penalties include fines which could reach $100,000.

Pet owners no longer wanting their fish are asked to contact fish hatcheries, Alberta Fish & Wildlife, or the store where they puchased the fish, or to euthanize the fish themselves, as well intentioned releases could have a long lasting impact on the province’s rivers.

“Invasive species are an issue forever,” said Meagher. “It’s really hard to get rid of them. You can’t really put a poison in (the water) for one species of fish, it doesn’t work that way.”

Big Al's Pet Supercentres sells a lot of pond fish and the retail store allows customers 'end of season' options.

"We let them know that they can bring them back into us at the end of the season, as long as they are healthy and we'll offer them a trade in value," said Brandon Verner with Big Al's.

With files from CTV's Kevin Green