First I saw the tooth marks. Walking at the Montrose Beach Dunes one morning in November 2020, I noticed some tree stumps clustered along the edge of Lake Michigan. A foot or so above the muddy sand, each came to a rough-hewed point, like the end of a pencil sharpened with a knife. Inch-square wood chips were scattered nearby. Surely, I thought, this must be the work of beavers. I imagined the big rodents spitting out those chunks as they gnawed through the trunks, knocking down these willows and hauling them away. But where had the beavers gone?

During that pandemic year, I’d been spending more time watching the city’s wildlife. But I’d never seen beavers outside of a zoo. And I didn’t know much about them. I soon learned that they construct their homes out of branches and mud. These lodges are often located on the bank of a pond, with an underwater entrance. Gazing around the Montrose Beach Dunes — best known as a summer nesting ground for those beloved piping plovers — I didn’t see anything that looked like a lodge.

After a few months of fruitless hunting, I received a tip on Twitter from a fisherman with the username @mrbigstevo. He said he’d often seen a beaver swimming at 3 or 4 a.m. along the walls of Montrose Harbor — half a mile from the dunes where I’d been looking. The animal “would hop out and go back into the golf course over there,” Mr. Big Stevo told me, referring to the nearby Sydney R. Marovitz Golf Course.

Sure enough, at the pond on the course’s north end, I spotted a mound of branches. Those branches hadn’t just floated to that spot — something had arranged them into a structure roughly a dozen feet wide. That must be where the beavers live, I thought. But to catch a glimpse of these mostly nocturnal creatures, I figured I’d need to get up before sunrise.

When I arrived one morning in April 2021, the eastern horizon was turning pink but the sky overhead was still dark. At 6:06 a.m., I spied something moving across the pond’s surface. In the low light, it looked almost like a log, but it had eyes and ears. By the time the sun rose at 6:23, the furry creature had submerged itself, vanishing from sight. My pictures of it were dark and grainy, and I wondered if it might be a muskrat, a mammal that can be mistaken for a beaver. But when I posted my photos on Twitter and the app iNaturalist, other people verified the species. “In short, sir, you have seen a Beaver!” @gregpyke46 tweeted. This would be the first of my many such encounters — 54 over the next three years, to be precise. I kept a detailed tally of my sightings. Isn’t that what any normal person would do?

“No animal has been more important to the natural and social history of this region than the beaver,” Joel Greenberg wrote in his 2002 book, A Natural History of the Chicago Region. Indeed, these engineers of the animal kingdom transformed the land, building dams that created ponds and wetlands. And their dense, water-repelling fur was highly desired by humans, who turned those pelts into fancy hats. But trapping — and destruction of wetland habitats — decimated the species. By the time Chicago became a town in 1833, the wood-chomping rodents were getting scarce here, and by the end of the 19th century they were entirely gone.

Since then, they’ve made a comeback, thanks to some human assistance. Federal and state officials reintroduced them in Indiana and downstate Illinois between 1929 and 1938. Later, even more beavers “were liberated on Cook County Forest Preserve District land in the Palos area,” according to Greenberg’s book. They eventually crossed into Chicago. “They’re one of those species that’s figured out how to navigate the city,” says Liza Lehrer, assistant director at Lincoln Park Zoo’s Urban Wildlife Institute.

A couple of months after my first predawn glimpse of Castor canadensis, I finally got a good look at one. I was sitting along Montrose Harbor on a June evening, hoping that a beaver might come out of the bushes — someone else had posted a photo of one walking in the vicinity. And lo and behold, a beaver suddenly burst into view, trundling toward the harbor. It was a few feet long and rather rotund. I wondered if it might be the single biggest rodent residing in the city of Chicago. You think we’ve got big rats? They’re minuscule compared with this guy or gal.

The beaver lumbered onto the harbor’s ledge — right past a no-swimming symbol painted on the concrete — then plopped off it with a splash. Once it was in the water, it glided gracefully, guiding its bulk by swishing its flat, scaly tail. After pausing by some boulders, it headed east into the harbor. I hurriedly walked over to the opposite end, where I received astonished looks when I asked a few strangers, “Hey, did you just see a beaver?” Then I noticed a man and woman pointing at a furry head moving across the water’s surface between the boats. They were surprised to learn that Chicago has beavers.

At least two lived in that pond. Were they a couple? Maybe — but it’s quite hard to tell male and female beavers apart.

Over the next months, I often looked through the chain-link fence by the pond at sunrise or sunset, when they were likeliest to be visible. After swimming around and around, they would shake the water from their shiny, oily fur. They spent a good deal of time chewing wood with their orange incisors or snarfing leaves from front paws that resemble a cartoon animal’s almost-human hands. The beavers didn’t have the pond all to themselves: Ducks, muskrats, and a snapping turtle sometimes joined them in the water, and black-crowned night herons occasionally stood atop their house. Not far away, human beings hit golf balls.

I tried not to disturb the beavers as they went about their business, but they often sensed my presence, staring intensely toward me with their inscrutable, dark eyes. I felt a little guilty the few times they slapped their tails against the water, making the splashy blast that serves as an alarm to their beaver comrades.

I worried I might look suspicious whenever I emerged from my observation positions inside the shrubbery, carrying a camera with a long lens. But on one such occasion, a woman who was jogging past said: “Seen the beavers? Are you Robert? I follow you on Twitter.” Thanks in part to my social media posts, the Montrose beavers had a growing fan base. Sarah Vogel, a local birder I’d met during my nature walks, was among those keeping an eye on these furry mammals. “Were they imagining making the golf course pond a better place, even if it conflicted with what the golf course might want?” she wondered out loud.

At first, I wasn’t certain if these were the same beavers that had chewed up those trees at the Montrose Beach Dunes, but that was the simplest explanation. I’d seen the golf course beavers swimming out of the harbor’s mouth, heading in that direction. To reach the dunes, they’d have to swim a mile and a half, looping around the Montrose Point peninsula and its pier. In the summer, they often swam up and down the little inlet separating the dunes from the pier. One evening, some children wading in the water squealed when they saw a furry creature speeding toward them like a torpedo. Cue the Jaws theme.

In the pier’s metal wall, I noticed a rectangular hole a couple of feet wide, which the beavers were using to hide out and pile up wood. I once saw a leafy bunch of branches way out in the lake — a good thousand feet or more from shore — moving toward where I stood on the pier. A beaver was hauling in a sizable chunk of a tree. But where the heck had it come from? As the beaver got closer, I could see how it clamped its mouth onto the biggest branch while deftly maneuvering its arboreal cargo through the water.

When the weather got colder, the beavers built up a stockpile of branches in the pond, saving them for later meals. As the water froze over, they were probably hunkering down inside their lodge. The absence of golfers during winter gave me an opportunity to venture onto the course, where I found dozens of gnawed trees and stumps. Yikes.

For eons, humans have viewed beavers as destructive pests. In recent years, however, more people have come to appreciate what these animals do. “There is a big movement now to recognize the importance of beavers — even so far as reintroducing them into wetlands,” says Lehrer. “When they’re occupying a wetland, they’re dramatically improving water quality. They’re creating habitat for a lot of fish species, amphibians, aquatic insects, and helping to slow down wildfires.” But trees are important, too, and it was alarming to see so many of them falling victim to these toothy critters.

I grew concerned that the city wouldn’t take kindly to the destruction of so many trees. And then, one morning in June 2023, I saw something large and furry drifting in the lake near the pier. It looked an awful lot like a dead beaver. While puzzling over how it might have died, I thought about the other beaver. Was it alone now? Would it feel sad when its friend didn’t show up at the lodge? But over the coming months, other people told me they were seeing at least three beavers, including one or two that looked smaller. Were these the offspring of the beaver that had died? I couldn’t be sure. I finally witnessed a trio with my own eyes on Christmas morning: splashing and munching together in the golf course pond. But their residency was coming to an end.

Stephen Boisvert, another birder I’d met on my walks, sent me a message in January 2024: He’d seen a government van parked near the pond. A man was rooting around in the icy water next to the beavers’ lodge. When I stopped by later, a sign was posted: “Mechanical devices have been placed in the water to capture animals causing damage. These devices and the animals captured in them are property of the United States Government.”

I emailed the agency listed on the sign, Wildlife Services, which is part of the U.S. Department of Agriculture. Spokesperson Tanya Espinosa confirmed that the feds were working to evict the beavers on behalf of the Chicago Park District, which issued a statement in response to my inquiries: “In rare instances, the presence of certain species can have an incongruous effect on park operations requiring the District to take steps toward removal.” Mangled trees weren’t the only “incongruous effect.” Officials were also worried about the beavers’ digging at their lodge. “Burrowing into a bank can cause erosion of the shoreline,” Espinosa told me, explaining that this could cause the pond’s bank to collapse, damaging the nearby fence and gravel path.

She said her agency had trapped 12 beavers at various Chicago Park District sites over the previous two years. In most cases, she said, Wildlife Services “lethally removed” the animals. Instead of killing them, why not move them somewhere else? Espinosa said that beavers are difficult to relocate, because a growing population already occupies so much of the suitable habitat in Illinois — and those animals will defend their turf against interlopers from Chicago.

That warning sign at the pond disappeared after several days. A week later, I spotted a beaver swimming. I exulted: It got away! When I asked Espinosa what happened, she replied: “We conducted trapping operations for a week but took the trap down when we were unable to trap the beavers.” I passed this news along to Boisvert, who cracked, “City beavers are no dummies.” But my relief was short-lived. Trapping soon resumed.

In spite of my fears that all the beavers might be exterminated, a spokesperson for the park district, Michele Lemons. later told me that two were relocated. “There was an adult male and a juvenile, sex unknown,” she added. The third beaver I’d glimpsed must have escaped, but its whereabouts now are a mystery. I haven’t seen any beavers in that vicinity since the trapping restarted.

Was it really necessary to remove the beavers of Montrose Harbor? Elsewhere in Chicago, including Lincoln Park’s South Pond, humans and beavers have settled into a more peaceful coexistence. “They’re difficult to manage, but not impossible,” Lehrer says, explaining the zoo’s efforts to let beavers live alongside the pond’s Nature Boardwalk. “We’ve caged all of the trees that are valuable to us: established old trees and ones that would not regenerate quickly. We haven’t lost any valuable trees for several years now.”

Around sunrise one day at South Pond, I heard people excitedly discussing the beavers they’d seen on their walks. And I spied one in the water, nibbling on some greens, just a few feet from me. When my camera clicked, the beaver thwacked its tail against the water and disappeared into the depths. I got the message loud and clear: Danger! Human!