Dumping your pet goldfish into the lake if you can no longer take care of it is not really a good idea. That seemingly harmless fish that you leave in a nearby body of water may actually become an invasive species.

Invasive species can wreak havoc on the ecosystem if they are introduced in a territory where their natural predators are not found. Their presence can have significant impact on the local resources and even kill important species.

Some of these invasive species started out as pets and the popular goldfish is one of the creatures that can potentially pose a threat to the ecosystem.

In a new study, researchers in Australia found that football-sized goldfish in the Vasse River in the South West region of Western Australia have actually travelled great distances to get there. Although goldfish are native to eastern Asia, they are now considered as among the worst invasive aquatic species in the world.

These species of fish can enter river systems after they are thrown from aquariums into catchment lakes.

Study researcher Stephen Beatty, from the Centre of Fish and Fisheries, said it is possible that the fishes were once pets owned by kids whose family had been moving house, and the parents may have dumped the fishes in the local wetland because they did not want to take the aquarium with them.

Once the fish population becomes established in the wild though, eradicating them can be difficult. The presence of the invasive fish may affect water quality, disturb habitat, bring about new diseases and compete with native species.

"Once established, self-sustaining populations of alien freshwater fishes often thrive and can spread into new regions, which is having a fundamental ecological impact and are major drivers of the decline of aquatic fauna," said Beatty.

Beatty and colleagues used strategically placed acoustic receivers to examine the movement patterns of alien goldfish populations for their study, which was published in the journal Ecology of Freshwater Fish on Aug. 12.

Another scary thing about dumping goldfish into lakes or any other body of water is that they can reach enormous sizes once they are in the wild. The domestic goldfish Carassius auratus for instance can grow to weigh more than 4 pounds when it is released in major waterways that depend on the abundance of resources. Their feeding habits can also disrupt the native fish populations because they eat the eggs of their competitors.