These are the tools you'll need to extract sperm from some of the rarest trout in the world: a towel, a small glass dish like those used on cooking shows to hold chopped ingredients, gloves, fish tranquilizers and your thumb.

On a recent day, no fewer than ten biologists, staff members and volunteers wearing waterproof waders and various shades of park-ranger khaki gather at the Leadville National Fish Hatchery to do just that. The inside of the historic building is chilly and loud due to the constant rush of water cascading into the open-top fish troughs.

See also: How Colorado Became Ground Zero in America's Energy Wars

Workers use a net to transfer the fish to a bin filled with water and sedative. Swimming soon gives way to floating, and one by one they scoop the sleeping trout out of the bin and pat them down with a purple bath towel. Once an individual fish is sufficiently dried (water will activate the sperm, and active sperm can only live for twenty to thirty seconds), it's handed to a biologist tasked with cradling the fish's body in one hand and using the thumb of the other hand to stroke its underbelly in a downward motion, almost as if he were trying to squeeze the last bit of toothpaste out of the tube. If the biologist is lucky, a few drops of milky-white "milt" will dribble out of the trout, drip down its back fin and make a small puddle in the glass bowl.

The trout that the biologists are working with are the offspring of fish from Bear Creek just outside of Colorado Springs. The creek is home to the state's last known population of greenback cutthroat trout, which Colorado designated as the state fish in 1994.

At least it's the last known population as far as scientists can tell.

From the time the greenbacks were included on the first-ever Endangered Species Act list in 1973, state and federal biologists have worked diligently to preserve and propagate them. It's not that the greenbacks are more precious than any other cutthroat subspecies; it's that we came so close to losing them, explains Kevin Rogers, an aquatic-research scientist with Colorado Parks and Wildlife.

"It's more of a legacy thing," he adds. "This is part of our evolutionary history in the state.... I'd like to continue to fish for these things that belonged here."

Doug Krieger, a senior aquatic biologist with Colorado Parks and Wildlife, agrees. "In some ways, they're the canary in the coal mine," he says of endangered and threatened species like the greenbacks. "If you protect them, you've protected the environment."

But in 2007, a University of Colorado study cast doubt on whether the greenbacks they were saving were actually greenbacks at all. A follow-up study published in 2012 confirmed their worst fears: The fish they'd spent so much time on was actually a different subspecies of cutthroat trout. In other words, they'd been saving the wrong fish.

What's more, researchers concluded that the right fish live only in a narrow, four-mile stretch of shallow Bear Creek, and counts showed that there were only about 700 of them left. The discovery was a blow to the biologists who had spent their careers believing they were bringing a native species back from the brink of extinction.

But those who continue the quest to save this small, spotted trout with the brilliant red-orange streaks hope that their latest efforts will finally put the drama to rest. Since 2008, biologists have been raising greenbacks in hatcheries with the goal of increasing their ranks. They started with just 65 fish from Bear Creek, and thanks to the hard work of many talented thumbs, the population has grown to approximately 3,800 greenbacks living in captivity.

However, many of the hatchery fish suffer from deformities not seen in the wild: having only one eye, for instance, or two chins. The defects are thought to be the result of more than a century of inbreeding among the last surviving population. In Bear Creek, deformed fish often die. But in the hatcheries, where the fish are more pampered, they can live to adulthood.

Later this summer, biologists plan to release a thousand hatchery-raised greenbacks into Zimmerman Lake, about an hour and a half west of Fort Collins. The hope is that the fittest among them will survive and spawn a new generation.

"We hope we have the right answer now, but there's still a tiny part of me that's skeptical," Krieger says of the current recovery efforts. "I don't want to be so arrogant as to consider that we have the absolute final answer." Tall, thin and mustachioed, Krieger, a 33-year veteran of the state parks department, is an integral part of the web of people who are dedicated to -- and frustrated and fascinated by -- the greenback. His office shelves are lined with three-ring binders thick with conservation plans, his desk is home to a fish-shaped tape dispenser, and there's a fish-of-the-month calendar tacked to his wall. One of his most striking decorations is a framed Audubon-style drawing of the greenback cutthroat trout, Oncorhynchus clarki stomias. Krieger's print is based on the Bear Creek greenbacks and was commissioned after the 2012 study confirmed they were the real deal.

Scientists believe the subspecies originated on the Pacific coast and swam to Colorado over a period of at least a million years. Once they arrived, they settled in waters east of the Rocky Mountains and flourished there until the mid-1800s, when overfishing (sometimes with dynamite), pollution from mining operations and farms that diverted water from rivers to nourish their crops caused the population to plummet.

The greenback's promiscuity also contributed to its decline. In the 1870s, fish hatcheries began to open in Colorado to meet the demand from fish-hungry sportsmen and locals looking to feed their families. In addition to native fish, many hatcheries raised and stocked non-native species such as brook and rainbow trout. When those fish were let loose in the greenbacks' territory, they either replaced them or bred with them, creating hybrid species.

Stocking is also probably how greenbacks ended up in Bear Creek. Using handwritten records and old newspaper archives, Chris Kennedy, a biologist with the U.S. Fish and Wildlife Service and another greenback fanatic, pieced together the following account: In 1873, the U.S. Signal Service built a trail along Bear Creek to the top of Pikes Peak, where it planned to construct a weather station. The trail became popular with tourists, and an entrepreneurial man named Joseph C. Jones decided to homestead there. His plan was to build a hotel and restaurant to cater to the people making the two-day journey to the summit.

Some of those tourists wrote books about their travels, and one of them, My Mountains, by pastor and outdoorsman Roselle Theodore Cross, mentions Jones. In the book, which Kennedy found in a Colorado Springs public library, Cross recounts that he spoke with Jones on an 1882 visit to what became known as Jones Park. After their chat, Cross writes, Jones "strode back to the work of digging big stones out of his fish pond."

"So we believe those fish were up there by 1882, and this Jones guy stocked them up there," Kennedy says. It's unclear where Jones got the fish -- they could have come from one of two local hatcheries known to raise cutthroat trout, or Jones could have collected them himself -- but Kennedy is pretty sure where they ended up: the upper part of Bear Creek, which is separated from the lower part by a barrier that fish can't swim across.

Because of that barrier, Kennedy believes that the upper part of Bear Creek was historically fishless. The greenbacks were able to survive there for 130 years because the barrier acted like a prophylactic, preventing non-native species from getting to them and hybridizing their brains out.

But the fact that there were greenbacks in Bear Creek remained a secret -- at least to the folks who declared the species extinct in 1937. Twenty years later, fish believed to be greenbacks were rediscovered in Rocky Mountain National Park. There were still relatively few of them, though, which is why they were listed as endangered in 1973.

After more reportedly pure populations were found, the species's status was downgraded in 1978 to "threatened" -- which meant that anglers could once again catch the fish but would have to release them.

Over the next thirty years, the state and the feds worked to bring back the greenback. They used the purportedly pure populations to start greenback broodstocks and then released the offspring into the wild. The hatchery-reared fish were put into empty creeks and streams or into lakes that had been "reclaimed" -- meaning that biologists had moved all of the fish that were living there and then poisoned the water with naturally occurring chemicals to kill any remaining fish so the greenbacks could start fresh, without any competition.

A 1998 report from the official Greenback Cutthroat Trout Recovery Team -- which is made up of staff from the U.S. Fish and Wildlife Service, Colorado Parks and Wildlife, the U.S. Forest Service, the Bureau of Land Management and the National Park Service -- states that by the late '90s, greenbacks were living in 62 different locations and that twenty of those populations were "stable," which was the number needed to remove the species from the Endangered Species List. Not all of the stable populations were in the proper geographic areas; however, the team predicted it could correct that by the year 2000.

But science soon interfered with the team's triumph. In 1999, new genetic testing revealed that the fish used to start at least one of the broodstocks -- and thus, all of those fishes' progeny -- were slightly hybridized. In other words, they were not pure greenbacks.

So the members of the recovery team started over. Using the best science available at the time, they went looking for non-hybridized populations. They found several and began breeding them in hatcheries and then re-reclaiming waters to make homes for their offspring. They were on their way to twenty stable populations when, in 2007, increasingly precise genetic research indicated they were on the wrong track. Again.

"That's when I had to break it to my biologists," Krieger says. "'We may have to do this all again.'" Jessica Metcalf didn't set out to debunk decades of hard work. She came to the University of Colorado at Boulder in 2001 to earn her Ph.D. in ecology and evolutionary biology under the direction of professor Andrew Martin. At first Metcalf was interested in studying tropical birds, but she changed her mind when Martin told her about the tricky genetic mystery of the trout.

"It seemed like the management program could benefit from a rigorous genetic study," Metcalf says. "It also became clear during the project that this is a really important subject in Colorado and a lot of people really care about it."

Although biologists could tell whether a fish was hybridized, they didn't have a good understanding of the genetic differences between the various subspecies of native cutthroat trout, especially the greenback and the Colorado River cutthroat trout. Since the fish look similar, biologists often told them apart based on where they lived. As far as they knew, Colorado River cutthroat lived on the Western Slope, the greenbacks lived in eastern Colorado, and a subspecies called the Rio Grande cutthroat trout lived in the southern part of the state. A fourth subspecies, the yellowfin cutthroat trout, had gone extinct in the early 1900s.

Metcalf and Martin used several techniques to test the DNA of all of the reportedly pure greenback populations to the east and several of the Colorado River populations to the west. But instead of a neatly divided picture, they found a free-for-all. There were some of what they assumed to be greenbacks in the west and many Colorado River cutthroats in the east. In fact, the researchers found that more than half of the eastern populations that biologists thought were pure greenbacks were actually Colorado River cutthroats. In their journey to save the rare greenback, they'd accidentally saved the more plentiful Colorado River fish.

The reason for the geographical checkerboarding, the researchers hypothesized, was stocking. By the time the greenbacks were rediscovered in the 1950s, hatcheries had distributed more than 300 million cutthroat trout throughout Colorado, muddling the map.

And then there were the fish in Bear Creek, a trickling tributary flanked by popular trails. The genetics of those fish were so different from both the supposed greenbacks and the Colorado River cutthroats that the scientists nicknamed them "Weird Bear Creek."

Metcalf and Martin published their findings in a paper in 2007; it ended with a harsh conclusion: Efforts to save the threatened greenbacks had "failed to improve the species' status." The story was picked up by major news outlets, and Colorado became the butt of fish jokes worldwide. "Whoops! Trout restoration used wrong fish," NBC declared. The New York Times called it a "possible oops," and one U.K. paper wrote that biologists had been "cheerfully re-populating many of the rivers with the more common Colorado River cutthroat trout. Schoolboy error."

Metcalf is more gentle in her assessment. "The main point," she says, "was that things weren't what we thought they were. And the patterns we were uncovering meant we really needed to delve a little bit deeper."

To do that, Metcalf and Martin compared modern-day cutthroat trout samples to specimens collected by explorers between 1857 and 1889, before stocking was widespread. They found the specimens, floating in jars of ethanol, at places such as the Smithsonian Museum of Natural History and the Museum of Comparative Zoology at Harvard. The museums allowed them to snip off tiny, half-pinkie-nail-sized pieces of gill or bone and pack them in their luggage or mail them back to the lab in order to test the fishes' DNA. Though it was sometimes badly degraded, they hoped that comparing ancient DNA with modern DNA would answer two questions: Which fish were which? And where did they historically live?

"We could have never predicted that we would find what we found," Metcalf says. Instead of four subspecies, they found that Colorado had once been home to six types of cutthroat trout. Two of those types are now extinct. As for the greenback cutthroat trout, the historical samples showed that the subspecies was native only to the South Platte River drainage. And the only modern fish whose genetics matched it were the weird fish in Bear Creek.

"It's the only place that they've survived," Martin says -- and by strange means. "If they weren't stocked there by this guy in 1882, who [wanted] a place to go hang out and have fun and have fish swimming around, they'd be gone. They'd be totally extinct." Metcalf and Martin's second paper wasn't published until 2012, but efforts to save the Bear Creek fish began much earlier, before biologists really knew how rare they were.

"We knew we had something special," Krieger says, "but we didn't know quite what."

To be on the safe side, Colorado Parks and Wildlife outlawed fishing in Bear Creek in 2006. (Bans on camping and fires followed for fear that a wildfire would make the soil toxic to the fish.) Two years later, after a count estimated that there were about 700 fish living in the creek, biologists moved a little less than 10 percent of them to hatcheries in order to start a broodstock.

But one of the most significant threats has always been the sediment. The soil around the creek is crumbly, and the creek itself is small, spanning only two to three feet in some areas. Popular hiking, biking and motorcycle trails run alongside it and even crisscross the water in various spots. The bare ground of the trails, coupled with heavy use, makes it easy for the crumbly soil to erode into the creek, which isn't very deep to begin with. If the water becomes too shallow, it can mean trouble for the fish. Though small (adult greenbacks in Bear Creek typically grow to be about ten to eleven inches long), the fish need pools of at least a foot deep to weather the icy winters and dry summers.

In 2009, the Rocky Mountain Field Institute was hired to install traps to stop sediment from flowing into the creek. But the traps filled up quickly. At first workers removed the soil and piled it back where it came from -- only to find that it soon washed back into the traps. Last year they took a different approach, filling more than a thousand sandbags, wrapping them in tarps, labeling them and leaving them in areas where they posed no threat to the creek, with the intention of using them in future trail-restoration projects.

But what they're doing won't solve the problem, only keep it at bay, says Amber Shanklin, program director for the Rocky Mountain Field Institute. "The trail itself is the issue," she says. As long as the trails are there, the creek is in danger.

Ned Suesse has been riding the Bear Creek trails for nineteen years. An officer with the Colorado Motorcycle Trail Riders Association, a group that works to maintain motorized trails, Suesse loves them for the same reasons many people do. "That area is very close to Colorado Springs, and it's neat to be in such a wild experience so near to town," he says. "You can spend all day in an office and then go up and get a little piece of yourself back."

Suesse first heard about the unique fish in Bear Creek in 2008, when Krieger approached him for help in preventing the spread of a fish-killing parasite. The parasite causes whirling disease, which gets its name from the way that infected fish swim -- in a corkscrew, or "whirling," pattern. Krieger was concerned that whirling disease could be transported from contaminated streams to Bear Creek on the tires of motorcycles and mountain bikes, horses' hooves and other sources.

The motorcyclists sprang into action, Suesse says, applying for a grant to build seven bridges at creek crossings that would discourage trail users from splashing through the water. The project was a success, and the state and the feds soon realized the effectiveness of partnering with user groups, some of which have deep pockets and gangs of volunteers willing to work. So the agencies convened a roundtable that came to include members of the motorcycle group as well as Trout Unlimited, the mountain-biking group Medicine Wheel Trail Advocates, Friends of the Peak and others.

Though the user groups didn't relish making changes to their beloved trails, they understood the importance of saving the fish -- or at least the inevitability that something would have to be done to protect the subspecies. Bear Creek isn't the greenbacks' native home, but it is the one place that's proven hospitable to them, which puts it high on the list of habitat to protect. Rather than fight the government, many user groups decided to cooperate with the agencies to make sure that whatever changes were made would meet their needs. They worked together to do trail maintenance and make improvements, and even rerouted some of the most erosive trails. With help from the motorcycle group and others, the Rocky Mountain Field Institute produced a thorough report that suggested more potential reroutes.

"We don't want to be the guy that says, 'The fish are fine' -- and then the fish die," says Cory Sutela, president of Medicine Wheel Trail Advocates.

But much of that work came to a halt in 2012, when the Center for Biological Diversity sued the U.S. Forest Service for failing to protect the "critically imperiled" greenbacks in Bear Creek in accordance with the Endangered Species Act. The nonprofit, which has offices in several states but not in Colorado, singled out motorcyclists as the problem. "Motorcycles were really ripping up the trails," says Tim Ream, the San Francisco-based staff attorney who filed the lawsuit. When the Forest Service didn't respond to requests that it ban motorcycle use, Ream says, the center slapped the feds with a lawsuit.

The motorcyclists were incredulous. They'd been on board with helping to save the greenbacks since the beginning, and Suesse argues that there's no evidence that motorcyclists cause any more erosion than hikers, mountain bikers or equestrians. "The problem here isn't really the use of the trails," Suesse says. "The problem is the layout of the trails.... It's not clear to me that motorcycles deserve to be the villain."

The motorcyclists were further ostracized when the Forest Service quickly settled the lawsuit and agreed to close five popular trails to motorized use. The settlement agreement cost the feds $40,000 and required that they complete their own lengthy watershed assessment to include proposals for rerouting the trails around Bear Creek in order to better protect the fish, which by now were recognized as the last surviving greenback population.

That process isn't completed yet, and many users are frustrated by how long it's taking. Adding to the frustration is the fact that the entire trail network around Bear Creek was closed following the floods in the fall of 2013. Even though the closures had nothing to do with the greenbacks, "the fish got blamed for it all," says Janelle Valladares, a wildlife biologist with the U.S. Forest Service who's leading the watershed assessment.

Most of the flood-affected trails reopened in June. But that doesn't mean they'll stay open. The Forest Service expects to release its final report -- often referred to as the National Environmental Policy Act, or NEPA, assessment -- late this summer or early this fall. Valladares says they're currently working to revise the report to include suggestions from the most recent round of feedback after earlier drafts of the paper were posted.

The response, she says, was overwhelming: The Forest Service received more than 700 letters from users.

Many were in support of "Alternative B," which would aim to stabilize the soils and increase the creek depth through a combination of erecting buffers and barriers, closing some of the trails, and rerouting other trails so that they don't run directly parallel to the creek. The proposal includes building several sections of new trail -- a prospect that many user groups are excited about -- so that the total loss is equal to just four-tenths of a mile, Valladares says.

There are no estimates of how much the plan will cost, Valladares says, nor has the Forest Service figured out exactly who will do the work. But many user groups are willing to pitch in.

"People have committed to helping to build new trails," says Susan Davies, executive director of the Colorado Springs-based Trails and Open Space Coalition, one of the user groups in the roundtable. The Forest Service, she says, is "walking a tightrope. They have to follow federal regulations, but they do understand that in our area, those trails are an economic driver and are a reason a lot of us live here.... We don't want to lose any more."

Meanwhile, the U.S. Fish and Wildlife Service is trying to sort out just how imperiled the greenbacks are. Back when they were listed as endangered in 1973, biologists thought there were two wild populations with a total of fewer than 2,000 fish. Now there's only one wild population, with an estimated total of between 500 and 700 fish.

Leslie Ellwood, a U.S. Fish and Wildlife biologist based in Lakewood, is leading the effort to determine whether the greenbacks should be upgraded from "threatened" to "endangered." The process involves evaluating threats to their habitat, risks posed by disease and overfishing, and the detrimental effects that factors such as climate change could have on the species. It's a big undertaking replete with government reviews, which means it could take years before there's a clear answer.

Anglers don't want to see the greenbacks listed as endangered. David Nickum is the executive director of Colorado Trout Unlimited, which petitioned for the greenback cutthroat trout to become the state fish in 1994. Before then, the non-native rainbow trout held that honor. But Nickum says anglers thought it would be better to bestow it upon a hometown species -- especially one that could use some good publicity on its journey back from near-extinction.

If greenbacks are classified as endangered, anglers will no longer be able to catch them (though Ellwood says the feds are looking into allowing some catch-and-release fishing so they can study its effects on endangered cutthroats). Even though anglers can't catch them now because fishing isn't allowed in Bear Creek, Nickum says the hope is that fishermen will once again be able to chase them when more wild populations are established. After all, he says, there's something special about catching a native fish, even if you have to release it.

"Fishing for brown trout, fishing for rainbow trout is a lot of fun, but it's kind of like your family trip to the amusement park, going to Busch Gardens or Six Flags. You can go and have a great time, but it's fairly similar," Nickum says. "Catching a native fish is more like going on a trip to a national park, where you're seeing what's unique to that setting." Back at the Leadville National Fish Hatchery, the pack of scientists, staff and volunteers continues with its assembly-line spawning. Every now and then, tourists stop to watch: a group from St. Louis, a grandmother and her granddaughter (Grandmother: "That's his sperm!" Granddaughter: "Ew"), a family wearing matching hats.

"That guy gave up quite a bit," says Josh Nehring, a Colorado Parks and Wildlife aquatic biologist whose thumb is doing most of the dirty work. Another biologist sucks up the sperm with a scientific instrument that resembles a turkey baster and deposits it into one of several small plastic bottles filled with "milt extender," a solution that will make the fish's reproductive material go further. The bottle is put in a red cooler for later.

After the biologists make their way through all of the eligible bachelors, they break for lunch. The morning has been as successful as can be expected for these people-shy fish whose ancestors spent their lives in isolated Bear Creek. About half gave up the goods.

"I think you need to play some Rod Stewart," jokes Kennedy, of the U.S. Fish and Wildlife Service. "'If you like my body and you think I'm sexy...' Some mood music."

Kennedy is there to keep a tally of the greenbacks' deformities. Every time the fish-squeezers pluck another fish out of the sedative bin, they examine it and announce its defects so he can mark them in his notebook: "I got a one-eye and a double-chin!" "Sounds like Chris's girlfriend," quips hatchery manager Ed Stege.

Kennedy and others hope that counting the deformities and eventually tracking the attributes of individual fish could help biologists decrease genetic defects in the population by breeding (or not breeding) certain greenbacks with one another, a method already practiced by many zoos and aquariums. "It's eHarmony for cutthroat trout," Kennedy says.

After lunch, the crew focuses on the ladies. The biologists wade into the fish troughs and employ the same technique on the female fish, using their thumbs to coax eggs from the sedated greenbacks. The females are much easier to "spawn" than the males: It only takes a stroke or two before a stream of fluid and yellow eggs, each about the size of a sequin, spray out of the female. The biologists collect the eggs in sandwich-sized Tupperware containers and then use a feather to gently tease out any specks of waste or eggshell. Once the eggs are clean, a volunteer uses the turkey-baster instrument to squirt a bit of sperm from the bottles in the cooler into the Tupperware containers. Mother Nature takes it from there.

By the end of the day, Krieger, Nehring, Kennedy and the other biologists have collected about 85,000 eggs. With any luck, a good portion of them will grow into greenback cutthroat trout that can be used to continue to populate places such as the reclaimed Zimmerman Lake, which has long been used for cutthroat trout restoration projects because of its remote location and the ease with which biologists can trap the fish there for spawning.

"Saving the world," Stege remarks as they clean up, "one cutthroat at a time."