In northern Michigan, the Glen Lake Association recently hired bowfishers to remove invasive koi fish from the lake — and, as it turns out, just in time. Three of the four koi removed from the lake were pregnant, meaning hiring the bowfishers prevented a wider spread of invasive species, MLive reported.

The Japanese koi fish may have been former pets released by irresponsible owners. They were easy to spot because they were bright orange, unlike any native species native to Michigan’s lakes, the news agency said.

“I knew more calls meant there were more fish in our lake and we needed to start doing something about it,” Rob Karner, the association’s watershed biologist, told MLive. “So we did.”

The largest of the four koi caught by the bowfishermen – a team from the Thundering Aspens Sportsman Club – was 32 inches long and weighed 25 pounds, setting a new world record for a Japanese koi caught with a bow, according to MLive.

Unfortunately, this is by far not the first case in which former pet koi ended up in a lake and caused devastating damage to the ecosystem.

The reason Japanese koi are considered invasive (as explained on the City of Savage Minnesota website) is because they are basically too good at being fish. Koi are hardy, can survive harsh winters, live to a very old age, reach enormous sizes, and eat vast amounts of food.

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This allows them to displace native species in a fight for resources and disrupt the balance of the ecosystem they are released into, according to ZME Science. They are also known to burrow into lake beds and uproot plants.

People’s circumstances often change, sometimes suddenly, but it’s still important to never release a pet into the wild if you find you can no longer care for it. If you ever have a koi fish that you can no longer care for, you should do everything you can to find the koi a new home by either selling it, giving it away, or contacting a local koi rescue organization.

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