“Because of their beautiful coloring and extreme hardiness, goldfish have become one of the most popular pets in the world,” Paul Paradise writes in a booster book for goldfish lovers. This is probably true, if goldfish can be called pets. But I think we humans have a much odder relationship with this comely little relative of the carp than we do with, say, Labrador retrievers. In my experience, when people bring goldfish into their homes it’s only a matter of days before the fish slip across the thin line that separates pets from decor. Yeah, goldfish are popular. But so are throw pillows.

Paradise gushes on: “So popular are they that they are given away at carnivals and circuses in games of chance!” As though this were a good thing. When I was little my cousin David spent a lot of hours at the goldfish booth at the summer carnival in Brazil, Indiana. About four feet behind the counter was a table filled with small glass bowls the size and shape of votive candle holders. Each bowl held one tiny living thing with a dull brain and a clever nervous system, floating in its own private ounce of colored water. The object of this game of chance was to shoot a Ping-Pong ball out of a cannon and make it land in one of the bowls. Mostly the balls bounced off the rims or missed them entirely. But many quarters later David succeeded in splashing a ball squarely into a bowl and was handed the container with the fish inside. He took the little orange creature home that night and set it carefully on our grandmother’s dining-room table. It almost seems superfluous to mention that when he awoke for breakfast the goldfish was floating belly-up in the violet water.

Around 300 years ago the Chinese pulled some gold-colored mutants of the crucian carp out of the sluggish streams where they lived and began to breed them, favoring the bright orange color. The goldfish we have around us today are descendants of these wild carp. Most of what we see in pet stores are the classic “golden” variety–the kind Pepperidge Farm used as models for its party snacks. But along the way breeders also cultivated varieties with bizarre features. Take for example the kind that has its eyes situated so that it’s impossible for the fish to see any direction except above it. It’s called the “celestial goldfish” because it’s always looking up toward heaven. Adorable in theory, but in practice this forces the fish to swim awkwardly with its head down to see where it’s going. Another favorite of goldfish fanciers, the “bubble-eye,” has translucent globs stuck on each side of its face–thin sacs that hold the fish’s eyes but rupture easily. The “lionhead” goldfish has masses of grotesque nodules stuck to the top of its head. It has a gnarled body, a short protruding abdomen, a stubby tail, and no dorsal fin–all of which essentially cripple it in the water. Someone obviously found these traits beautiful and deliberately selected for them in breeding. These exotic varieties are highly prized and fetch higher prices than the ordinary golden variety. But you’d have to think twice before swallowing one of these guys at a frat party.

Until very recently this was the total of my experience of goldfish: they served only as props, prizes, or genetic freak shows. So the idea that I could see schools of goldfish in the wild in Chicago seemed about as likely as finding a coffee table running free in the forest preserves. But it turns out that thousands of ordinary golden-variety goldfish live very happily far outside the tanks in Woolworth’s pet department, in Chicago’s streams and rivers. Like the Savages in Brave New World, these daring fish forage for food, reproduce, age, and die more or less naturally, all while removed from the ghoulish rule of civilization. In the opaque, olive-colored channels of the Chicago River the Savage goldfish have managed to carve out lives for themselves by eating algae, sludge worms, nematodes, leaves of plants, and whatever else comes their way–even as they try to avoid being eaten themselves by the herons that patrol the river’s banks.

I know this because I saw them. I was canoeing the North Shore Channel, a straight canal that runs from the Baha’i Temple in Wilmette to North Pier downtown. I was goofing around for the day with Laurene Von Klan, who spends a lot of time on the water for fun and in her job as director of Friends of the Chicago River. The day was mostly overcast, but occasionally the sun would come out and spotlight a black-crowned night heron on the shore or a television set floating in the water. In a patch of sunlight ahead of me near the Foster Avenue bridge I spied a bunch of red flashes near the surface of the water. I didn’t know what they were, but Laurene recognized them immediately. “Goldfish!” she hollered.

Like a tourist boat chasing dolphins, we paddled up close, right into the school. From where I was I could count 40 goldfish, and more appeared to be swimming deeper. They ranged in size from finger length to the size of my hand. We watched them swim, nibble weeds, nudge each other, and just be goldfish, until some girls kicked a soccer ball into the water near us and we interrupted our observation to retrieve it for them.

One or two of the fish seemed to be having difficulty breathing and kept appearing to gasp air at the surface. When I later mentioned this to Sam Dennison, an ichthyologist for the Metropolitan Water Reclamation District, he explained that fish that do this are still breathing water, but they’re trying to take in water right at the surface, where it has the greatest quantity of dissolved oxygen. Generally speaking, goldfish do well in waters so low in oxygen that other fish can’t survive. Which is why they can live in goldfish bowls, an arrangement that would kill a tetra or molly. They don’t usually need the extra oxygen put into the water by the aerators in aquariums, though they might be happier with it.

Goldfish, it turns out, are remarkably common in the Chicago River. Dennison says that when the Water Reclamation District takes samples of fish life in the river, over 90 percent of the weight of the catch is carp, goldfish, and carp-goldfish hybrids. How they got in the river in the first place is unclear. We know that at the turn of the century well-intentioned park planners released goldfish in the lagoons and ponds of Chicago’s grand parks. But to get into the Chicago River these fish would have had to travel from the Lincoln Park lagoons out into Lake Michigan, an inhospitable habitat, and over to the mouth of the river. Another theory is that in the days when household sewage drained into the river, flushed pets might have made it through the system and survived. When I asked Dennison about this possibility he said in his dry voice, “That’s a theory. I’ve never tracked a fish that way though.”

The water in the Chicago River is much clearer and cleaner than it has been for a long time due to aggressive cleanup efforts by the Water Reclamation District and strong environmental-protection laws. And the hated zebra mussels are making the water even clearer. Still, 2 to 5 percent of Dennison’s catch is usually carp-goldfish hybrids, which indicates that the water is murky enough that the carp and goldfish apparently can’t always see well enough to tell whom to mate with. (A problem humans who’ve spent time in some of our darker and scarier singles bars may empathize with.)

Unlike a lot of alien species, this Asian fish doesn’t seem to pose any significant ecological threat to other aquatic creatures. Dennison describes the goldfish as “opportunistic, but not a good competitor.” They are plentiful in bad water, but as soon as the water quality improves and other fish can live their numbers decline. Downstream from where the Chicago River joins the cleaner Des Plaines River, juvenile goldfish are absent. Illinois Natural History Survey researchers believe widemouthed bass eat them. Any animal that’s a “sight-feeder,” one that finds its prey by seeing it, will quickly pick up and devour the poorly camouflaged goldfish. But until the Chicago River becomes cleaner and more hospitable for more species of fish, may all the Savages live long and prosper.