The Great Lakes in the area of the United States and Canada are the largest group of fresh water lakes in the whole world. Because the five lakes are connected to each other, aquatic animals can freely communicate in them. This makes the spread of some invasive species portable, and because the Great Lakes are not in the same country, which makes it extremely difficult to control, the invasion of the Great Lakes in North America has been very serious.

Among the worst invaders are the Asian carp, which can grow up to 50 kilograms in the Great Lakes and cost millions of dollars to control each year, and the zebra mussel. Zebra mussels are even more frightening. The mussels can grow so fast in water intake pipes that they clog them. They have forced the shutdown of nuclear power plants several times because of this property, and it costs Canada (28% of the Great Lakes area) about $250 million a year to clean the zebra mussels from the pipes.

However, there is another humble but horrible animal that has also been causing distress and disorder to the native species of the Great Lakes in North America, and that is the goldfish - the kind of pet goldfish that we usually have, is not surprising. A 2018 count put the number of goldfish in Lake Ontario, the smallest of the five Great Lakes, at 40-50 million, and while they don't like to destroy human facilities as much as zebra mussels, they don't grow as big as Asian carp (which are believed to make up about 50% of all fish by weight in some North American lakes), However, the destruction of the goldfish to the ecology of the lake can not be underestimated, because their behavior is too bad.