Standing waist-deep and casting a hand-tied fly earlier this month, he pointed to his favorite deep pool. "This is the honey hole," he said.
Here, the fish are big. The strikes are frequent. And other anglers are kept at bay by the occasional bobbing diaper.
Mr. Teasdale's fly-fishing hole is on the South Platte River, at the mouth of a 6-foot-wide corrugated-metal drainpipe and downstream from a wastewater-treatment plant. The water has elevated levels of E. coli bacteria, according to government surveys. When Mr. Teasdale walks alone past the graffiti-covered overpass and down the littered trail in this Denver suburb, he brings his Glock 9mm pistol to ward off "shady characters."
Mr. Teasdale is a "brownliner," one of the growing ranks of fly fishermen who try to catch whatever lives in the muck close to home -- in drainage canals, cemented urban riverbeds and murky farm-runoff canals. Another of Mr. Teasdale's favorite spots is a muddy stretch of river behind a strip mall.
Brownliners enjoy fly-fishing's primary perks -- the suspense of watching a fly disappear beneath the water's surface, the struggle of man against beast, the spinning of fish stories. If that doesn't come with fresh water and clean air, so be it.
The pursuit is an affront to fly-fishing's traditional ethos. Since English nobles began using bamboo rods and whiplike lines to cast weightless flies to trout, the sport has been associated with pristine wilderness. "More than half the intense enjoyment of fly-fishing is derived from the beautiful surroundings," angling legend Charles Orvis wrote more than a century ago.
Mr. Teasdale used to fly-fish in the old-growth forests of the Pacific Northwest, casting for trout in ice-blue rivers. He released the fish he caught, out of respect for their beauty.
Now he spends about three days a week in water tainted by urban runoff. His quarry is often carp, a hardy relative of the goldfish with a suckerlike mouth and a coat of viscous slime. Mr. Teasdale, 26 years old, throws them back because he's afraid to eat them.
Mr. Teasdale isn't the first to loft a wet fly into an urban canal or algae-covered golf-course pond. But there was little unity among them until a Californian named Keith Barton started his blog.
Mr. Barton was a die-hard trout fisherman until about 2000, when he was driving between the Sacramento suburb where he lives and far-Northern California, where limpid trout streams drain the Cascade Range. Alongside the highway, Mr. Barton says, were farm ditches and stagnant creeks without a single fly fisherman on their banks. He had an epiphany. "You see a lot of water going by, and you say: 'There's got to be some fish in there.' "
Exploring waters redolent of manure and marked by signs warning of mercury contamination, he caught pikeminnow, carp and bass -- species that traditionalists look down on as "coarse" fish. Mr. Barton soon realized that, whether a trout or sucker, "It swims away from you, which is really the only thing that most fishermen want."
Mr. Barton helped coin the name for his sport two summers ago. He recalls that a fly-fishing friend, Tom Chandler, called him to talk about "bluelining" -- scanning a wilderness map for the squiggly blue lines that represent remote streams and hiking into those valleys with a fly rod. Mr. Chandler had spent the day fishing in a cold, clear trout stream fed by Mount Shasta glaciers.
Mr. Barton had spent the same day casting his line into a slough littered with sofas, old cars and goat carcasses. "I told him what I'd just wiped off my shoes," recalls Mr. Barton. During that conversation, he says, the men first talked about the term to describe Mr. Barton's fishing.
Mr. Chandler began talking about brownlining on his blog, troutunderground.com. Mr. Barton soon started his own blog, Singlebarbed.com.
Brownlining has since caught on among others. In Minnesota, fly-fishing guide Jean-Paul Lipton sells brownlining flies on his Web site; he charges anglers $250 a day to pursue turbid-water species like white suckers. In Los Angeles, Sean Fenner ducks under the Glendale Boulevard overpass to cast for carp. Mr. Fenner called the Los Angeles River's concrete-lined channel -- seen in car chases on TV shows and films including "Terminator 2" -- an "underutilized body of water for fly-fishing."
In Glasgow, Alistair Stewart fishes for trout in holes on the River Kelvin known locally as Sanitary-Towel Pool and Petrol Pool. "There's this overwhelming smell of petrol when you're fishing it, and no one knows where it's coming from," he says. Though the river is cleaner than it was when dye plants operated on its banks decades ago, Mr. Stewart says he finds mannequins, spools of fiber-optic cable and "loads of shopping trolleys" in it.
Traditionalists would never make do with dirty rivers. Jeff Bright, a San Francisco photographer who flies into the Canadian wild to fly-fish for steelhead trout, says the wilderness lends an "almost spiritual" aspect to fly-fishing. He worries that abandoning that idyll to fish in polluted waters amounts to "sanctioning" nature's destruction.
That's fine with brownliners. "I count on their elitism to keep them away," Mr. Teasdale said as he headed from a suburban Denver parking lot toward his honey hole.
Mr. Teasdale's fishing partners this day included Kyle Deneen, one of three corpulent authors of the Fat Guy Fly Fishing blog. Mr. Deneen lives on the bank of a famous Colorado trout stream, but he drove two hours to join Mr. Teasdale's waste-water expedition. "I wanted to fish for carp," said Mr. Deneen, who has the Fat Guy Fly Fishing logo tattooed on his forearm.
Also along on the trip was Michael Gracie, a Denver tech consultant, who met Mr. Teasdale at Denver's Discount Fishing. Mr. Teasdale manages the shop, where he offers novices advice on where to fish and sells brownlining flies that imitate a carp's diet of crayfish, muck-dwelling insects and cottonwood seeds.
Messrs. Teasdale, Gracie and Deneen walked past a pile of crumpled beer cans into a slow-moving section of brown water. Standing on blocks of broken concrete, they set up beneath the drainpipe. Discarded tires dotted the riverbed. On warm summer days when families have picnics upstream, Mr. Teasdale said, diapers often bob down the river.
Mr. Teasdale cast upstream and let his flies sink to the bottom. His fly rod doubled over when he set his hook. "Oh, it's a big one," Mr. Gracie said, stumbling around to net the fish as it swam in circles. "It's a channel catfish!" Mr. Teasdale exclaimed. He'd never caught one here before.
"It's about 10 pounds," he said, releasing the fish.
Back at his fly shop at the end of the day, the storytelling began. "I caught a 15-pound catfish," Mr. Teasdale announced.