It's kind of like an amazing dream coming to life. Your adorable little goldfish grows into a giant, chasing you around a pond.

Only in this case, 11-year-old Luke Hebb wasn't dreaming when he fished a 16-pound koi out of Lacombe Lake in St. Albert Wednesday morning.

"I thought it was little at first, but then we weighed it and it turned out to be massive," Luke told CBC News Thursday of the 30-inch long monster.

Luke and his grandfather, Robert Aloisio, go fishing together a few times each year.

The pair were out searching for crayfish Wednesday when they hooked some hot dogs to their fishing line for bait at the lake in a northwest St. Albert park.

"We set two lines because we knew there was koi in the lake," Aloisio said. "Luke had quite a tussle with that fish. He brought it around to the shallow end and he jumped in the lake and rassled that thing up."

How Luke Hebb and his grandfather, Robert Aloisio, fished an invasive 16-pound koi out of a St. Albert pond. 1:47

Despite his young age, Luke caught another big koi — 14 pounds — in the same lake a few years ago.

"They're just getting huge and they're taking over that little pond," said Aloisio.

Luke had quite a tussle with that fish. - Robert Aloisio

While the Alberta Conservation Association stocks the lake with rainbow trout, ornamental carp — goldfish and the larger koi — often find their way into the pond by way of abandonment.

"Quite often people do not want an aquarium anymore and they don't know what to do with the fish … so they think releasing it into a water body is kind of a harmless way of getting rid of it," said Melissa Logan, the City of St. Albert's environmental co-ordinator for the Sturgeon River and natural areas.

"Unfortunately it's not the best for our ecosystem."

Goldfish cull in September

Last week St. Albert said it will use a chemical called rotenone to kill off the goldfish population in the pond. Logan said there will be two rounds of treatments during September.

In 2017 the city treated the Edgewater Pond and a water body at Ted Hole Park, killing nearly 45,000 goldfish.

St. Albert has been battling to get the koi population under control for the past decade. Of more than 20 ponds in the city, koi have been found in only three.

Logan said while the fish are invasive to the city's ponds and lakes, the real concern is goldfish getting into the nearby Sturgeon River.

"The stormwater ponds actually have a direct connection to the river," she said, adding there's also the possibility of a bird dropping a small koi into a stormwater pond or the river itself.

The city is working with Alberta Environment to promote a campaign called Don't Let It Loose. It's aimed at educating people to bring their unwanted fish to pet stores instead of abandoning them in local water bodies.

Logan said all species of fish in Lacombe Lake are fair game to anyone who takes them out, but they must be dead before leaving the area.

As for the future of the koi Luke caught, he's hoping to save enough money to get it mounted. Until then, it's in his grandfather's freezer.

"I'm trying to call around to see if we can get a deal on it or something because it's probably going to cost around $700," he said, adding that he may need to find a job to help pay for it.