How massive, feral goldfish are threatening the Great Lakes ecosystem

GEOFF BENNETT: For many people, it's their first pet, the humble

goldfish

.   Swimming in a tank in your house is hard to imagine being much of a threat. But when released into a large lake, a

goldfish

can endanger the fragile

ecosystem

of the world's largest freshwater system. Christopher Booker has the story. ANDREA COURT, Wetland Restoration Ecologist, Royal Botanic Gardens: Yes, you can pull the bottom board. CHRISTOPHER BOOKER: Environmentalist Andrea Court is starting another day at Cootes Paradise Fishway in Hamilton, Ontario. Located between Lake Ontario and Cootes Paradise Marsh, this fish zone acts as a boundary wall for fish.

The goal? Keep invasive species out of this marsh, an important spawning and nursery area for native fish. ANDREA COURT: We have a series of baskets or cages that are underwater. So we have a crane. He lifts the basket, throws them into a container and then we sort the fish. At that point I can decide which direction the fish are going to go. CHRISTOPHER BOOKER: With a flick of the wrist, Court sends native fish, like this channel catfish, into the marsh to spawn.  Invasives, like this common carp, are not so lucky. ANDREA COURT: In recent years we have rejected between about 2,000 and 9,000 carp.

CHRISTOPHER BOOKER: And when you say go away, you give them back? ANDREA COURT: Yes, I send them back to the port, yes. They are denied entry to the swamp. CHRISTOPHER BOOKER: When the fishing route began operating in 1997, the main concern was invasive carp, whose population exploded in the swamp, displacing native fish and depleting aquatic plants. But in the last decade, as carp populations have declined, a golden icon of children's pets has made waves. ANDREA COURT: So here we go. Here's a goldfish. It seemed like we got the carp out and the goldfish moved in. So starting in 2013 was really when we started to see more numbers, a

great

er number of them.

CHRISTOPHER BOOKER: But these goldfish don't look like the friendly little ones swimming in the tanks at the local pet store. Even its characteristic color, bred in captivity, can disappear in the wild. This is a goldfish, but it is not gold. ANDREA COURT: Well, it's not very advantageous to be bright orange in nature. And so this   is more of his natural color. Obviously it can be much more camouflaged. CHRISTOPHER BOOKER: Goldfish, kept in a container and fed a controlled diet, make small, simple pets. But when they are released into

lakes

and ponds like this, they gain access to an endless supply of food and can become large, destructive pests.

JON MIDWOOD, research scientist, Great Lakes Fisheries and Aquatic Sciences Laboratory: They grow quite a bit. So I think the world record is nine pounds, you... CHRISTOPHER BOOKER: Nine pounds? JON MIDWOOD: Nine pounds. (LAUGHTER) JON MIDWOOD: But the biggest one we've seen here is about 40 centimeters, so about half that size. CHRISTOPHER BOOKER: Jon Midwood is a research scientist at the Great Lakes Fisheries and Aquatic Sciences Laboratory. He says these wild goldfish, which researchers estimate could number in the tens of millions in the Great Lakes alone, most likely originate in domestic fish tanks. JON MIDWOOD: What we think is happening is that people have goldfish at home, they have them in their aquarium, and when they're done, they don't really know what to do.

And then they release them into the natural environment, because they don't want to kill that fish that they love. The same characteristics or adaptations of goldfish that allow them to really thrive at home, in the sense that that container that sits on a shelf and doesn't get new water for a while, isn't cleaned, those same adaptations allow them to thrive. in these systems that are quite degraded. CHRISTOPHER BOOKER: He says goldfish not only compete with native fish, they literally muddy the water around them. JON MIDWOOD: What goldfish can do is disturb the substrate or the sediment and mix it up, and it gets all cloudy and murky, and that stops vegetation from growing.

They are one of the most difficult fish to keep in the system. There are other aquatic invasive species here, but we think goldfish are likely to have the biggest impact in the near future on that goal of trying to recover aquatic vegetation. CHRISTOPHER BOOKER: Midwood says he would like to see these invasive goldfish culled, but there is simply no safe, affordable way to do so, because of the pollutants they carry when they feed at the bottom of an industrial waterway. JON MIDWOOD: Those fish pick up a lot of those pollutants. And so if you're trying to dispose of them, there have been challenges in the past in terms of where to dispose of them.

Because they have large concentrations of things like PCBs and metals. Once an invasive aquatic species is in your system, you can't do much more than try to keep their numbers down. Therefore, the best way is really prevention. CHRISTOPHER BOOKER: But pet owners struggling with unwanted fish often face a dilemma. NEILEE IRWIN, fish owner: I asked some people who had ponds if they wanted them, but no one wanted them, so I didn't really know what I was going to do with them. CHRISTOPHER BOOKER: Across the border in Erie, Pennsylvania, Neilee Irwin was the reluctant owner of a goldfish with an unusual name who she was quickly outgrowing her tank.

NEILEE IRWIN: They called him That One, because every time someone came into the house, she would just say, "That One." And I said, yes, that's her name. He is the biggest. CHRISTOPHER BOOKER: Under the right conditions, goldfish can live 30 to 40 years. And this can leave their owners in deep water. That's why the Erie Zoo started a one-of-a-kind pet project last year. HEATHER GULA, Director of Education, Erie Zoo: This is the last chance loophole. This is the main pond. CHRISTOPHER BOOKER: The Last Chance Lagoon offers unwanted goldfish and koi a luxurious new home, a 23,000-gallon tank in the heart of the zoo.

But according to Heather Gula of the Erie Zoo, the project's primary function is to educate the public. HEATHER GULA: We want to teach them about invasives because they are a big problem in the Great Lakes. We also want to teach them about proper pet care and expectations. That's something that many zoos work to educate the public about, because there are many people who want exotic pets or bring in some that they simply don't know how to care for. CHRISTOPHER BOOKER: Last Chance Lagoon intake forms tell the story of fish owners' woes. HEATHER GULA: This one is called Pumpkin Bob.

The owner did not know how long they would live. They got Pumpkin Bob at a fair and he lived in a one-gallon tank. CHRISTOPHER BOOKER: Along with about 50 other fish, Pumpkin Bob is now tankmates with Irwin's That One fish, which has been living in the lagoon since last fall. HEATHER GULA: That's it. Be free. NEILEE IRWIN: They needed something better. So I was very, very grateful, very grateful to be able to put it here and now I can visit it. CHRISTOPHER BOOKER: One less goldfish to wreak havoc on nature. For "PBS NewsHour," I'm Christopher Booker at Last Chance Lagoon in Erie, Pennsylvania.