There may be plenty of unwanted fish in the sea for government ecologists, but often those invasive aquatic species are a boon to local anglers.
Take the brown trout. A European native, the trout was introduced into America in the late 19th century and can now be found in bodies of fresh water from coast to coast.
Though they may might provide tasty meals after lazy summer afternoons, new fish species come at a cost greater than a bucket of worms.
"There's a number of either purposely introduced, or accidentally introduced, species that have provided quite a recreational resource," said George Madison, fisheries supervisor for the Michigan Department of Natural Resources for the Western Upper Peninsula. "So while smelt can be desired by people, or brown trout or rainbow trout, it's very clear that they out-compete the native species."
In the Great Lakes region, the introduction of salmon has changed the aquatic landscape, displacing native fish such as the coaster brook trout, a minnow forager.
As larger fish destroyed the vegetation, the minnow population declined, spelling doom for the coaster brook trout.
Near Provo, Utah, residents stocked Utah Lake with carp in the 1890s for fishing.
"Now they make up well over 90 percent of the biomass of that lake," said Scott Root, the conservation outreach manager at the Utah Division of Wildlife Resources.
His agency actively looks for ways to get rid of them.
Carp also cause headaches for Bob Davis, an area fisheries supervisor at the Wisconsin Department of Natural Resources.
"That's the single biggest problem with invasive species that we have," Davis said. "The carp really has no natural enemies. With its feeding habits, it uproots the established vegetation in the lakes and streams and clouds the water and makes things undesirable for many other species."
Stocking your pond with an exotic fish might make for a fishing challenge, but it's also likely to cause an epic ecological battle that may never be won.
"I'm always reminded of dandelions," Madison said. "Evidently they were brought over by a European who wanted to enjoy dandelions when he came to the United States — and you see the great field of dandelions we have now."