In short, setting your pets free could do more harm than good - so don't do it.
Here's the proof:
A handful of goldfish were released into a lake in Colorado. Now, much to the dismay of locals, there are thousands of them living there.
Goldfish are actually part of the Carp family and are native to Japan, so have no natural predators in America.
They have the potential to spread viruses and, if they escape lakes and head downstream, they could out-compete native fish (some of which are already threatened).
Removing these species also costs the government a lot of time and money.
In 1890, a fan of William Shakespeare wanted to bring the birds from Shakespeare's work to his home in New York.
So, he released one hundred starlings into Central Park and by 1928 those birds had bred so much that the population reached the Mississippi river.
By 1942 they had spread all the way to California, forming flocks of as many as one million hungry birds, driving off native species such as Bluebirds and Woodpeckers.
Today there are an estimated 200 million starlings in North America costing £800 million in damage to the agriculture industry.
Lizards: Pythons and the Argentine Tegu
In Florida, 84% of all introduced species stem from exotic pets which have been released into the wild.
Some of these include the Argentine Tegu, a lizard which can grow up to 4ft in length and lay 45 eggs a year.
Once established in an environment, they'll compete with local animals such as cats and dogs, and even native animals such as raccoons.
Watch the video for more unwanted pets who've caused havoc in their new-found environments.