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Famed Stretch of Colorado's South Platte Devastated in Flash Flooding

Cheesman Canyon suffered "mind-boggling" damage after a deluge of rainfall on July 31.

Famed Stretch of Colorado's South Platte Devastated in Flash Flooding

Cheesman Canyon on Colorado's South Platte River, a world-famous section of trout stream, suffered significant damage after flash flooding roared through due a deluge of rainfall on July 31.  (Pat Dorsey photo)

The many miles and various sections of Colorado’s South Platte River are some of the most famous stretches of trout water anywhere in the world, with names like the Dream Stream, Deckers, and Cheesman Canyon. Pristine runs and riffles flow through high parklands, boulder-filled canyons, and more miles of riverbed than most will fish in a lifetime. The big, wild trout of the South Platte have tantalized fly anglers for years.

This week, however, a portion of the South Platte—namely the Cheesman Canyon section—suffered significant damage after flash flooding roared through due a deluge of rainfall on July 31.

"So bummed right now, words cannot explain how I feel,” said frequent Fly Fisherman magazine contributor and southwest field editor Pat Dorsey via e-mail. "Today, I walked from the Family Hole to just short of the Upper Narrows and the end result was 20 sediment slides and almost all the holes have filled in with decomposed granite. The hardest hit sections were near Johnson’s Camp and Rainbow Pool. The burn scar from the Hayman Blaze has never fully recovered and that was the nail in the coffin. I did not see many fish, but the water is still stained, nor did I see any dead fish, which is good news. But, insect-choking sediments are covering the substrate so I’m pretty sure that the bug life has taken a huge hit.”

Video provided by Dorsey of the storm and aftermath is shown below.

In addition to his regular contributions to Fly Fisherman, Dorsey is the author of several successful books, a well-known Colorado fly fishing guide, and co-owner of the Blue Quill Angler Fly Shop in Evergreen. Guiding on the South Platte for more than 30 years now, Dorsey has spent countless days guiding others and fishing himself on that familiar canyon stretch of the famed tailwater.

What he saw yesterday broke his heart.

Sediment flowing into a river.
Sediment resulting from recent flash flooding has filled in many famous holes in the South Platte River's Cheesman Canyon. The extent of the damage won't be known for weeks or months. (Pat Dorsey photo)

"I stood in this hole yesterday catching fish on Sparkle Duns," noted Dorsey. "Today this hole is covered in tons of gravel. The devastation is mind-boggling, words cannot explain it. My office is in shambles and our finned fins are under distress.

“The Pale Morning Dun hatches as of late have been epic,” Dorsey continued. “So many 16- to 18-inch rainbows were brought to hand and several nice brown trout too. Now only time will tell, but things look pretty bad…And the (really) bad news is Denver Water has dropped the flow to 75 cfs because there is so much water in the system and Strontia Springs and Chatfield are close to or over capacity.”




The flooding stems from monsoonal thunderstorms that swamped portions of the Centennial State on July 31. The Fort Collins Coloradoan showed numerous photos of the flood damage caused by overnight rains, including damaged cars, flooded restaurants and a hotel, and buildings on the campus of Colorado State University. Nearby in Wellington, neighborhood streets were swamped.

According to the Denver Gazette, much of the flooding rainfall was centered in the Front Range, where rain gauges displayed anywhere from 0.91 inches at Silverthorne to 4.40 inches in Wellington and 4.22 inches near Castle Rock. Many reporting stations had rainfall measurements in the 1- to 3-inch range.

On Tuesday, Dorsey’s dutiful social media reports also included a video reel that showed what transpired the previous day when those heavy rainfall rates descended upon his portion of the state.

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"Yesterday's flash flood in Cheesman Canyon was the worst storm I've ever seen in there," he wrote. "Words cannot explain the devastation that occurred to the fishery and the trail. The Gill Trail is trashed, there are sediment slides everywhere, many of which dumped insect and trout-choking sediments into one of America's finest wild trout streams."

Dorsey noted that he left the river the previous night as the flooding was occurring, hunkering down for an hour in the rock tunnel near Cattle Crossing. As he departed, the river was already running chocolate brown and oozing with sludge and flood debris.

“Heavy rain started at 4 p.m. and it poured for a couple hours,” said Dorsey. “The dam got 2.5 inches of rain in one hour, and I am convinced the area we were in (Cattle Crossing) got much more than that. 

"My fear is the fishery, I think it took a huge hit, and more weather is expected today, tomorrow, and the next day," he wrote on August 1 with the video. "We canceled all our guide's trips in there today because of the unknown and for obvious safety concerns. The gauging station went from 239 to 630 cfs if that gives you any idea of how quickly the river rose. Only time will tell the fate of this fabled fishery."

It’s worth noting that not every section of the South Platte was severely affected by the flooding, and the river isn’t immune from such natural challenges. The June 2002 Hayman Fire–the largest wildfire in Colorado history–sparked, eventually charring more than 137,000 acres–much of it along land surrounding the South Platte River and Cheesman Lake. The damage to the landscape and the South Platte fishery was immense.

A section of river cover in sediment.
Rainbow Pool washout. Peanut Rock completely covered by decomposed granite. (Pat Dorsey photo)

The river suffered greatly from the loss of trees, grass, and other vegetation, and the resulting ash, decomposed granite, and debris washed into the river from regular rainfall and snowmelt after the fire. Fish mortality was high and spawning success was impacted greatly.

Over time, the river slowly rebounded, and today, if you didn't know that the massive blaze happened, you might not recognize any of the signs. But, noted Dorsey: “This is as bad or worse than the flooding after the Hayman Fire.”

Flooding, while not common on the South Platte, isn't an unprecedented occurrence either, particularly near Littleton where Dorsey grew up. As you can probably tell, he  is intimately familiar with the famous trout stream, having fished it much of his life and literally writing the book on fishing the river with his stellar workt, the Fly Fishing Guide to the South Platte River.

"The picturesque, boulder-filled Cheesman Canyon section of the South Platte River is considered by many to be one of the most pristine trout fisheries in the world," wrote Dorsey in his book. "Cheesman Canyon is nestled between Pikes Peak to the south and the panoramic Rampart Range to the north. This area is often affectionately referred to as ‘the canyon’ by fly-fishing aficionados, and your journey here is an experience you will likely never forget.” 

While not every section of the river is prone to the type of flooding that happened earlier this week, the closer one gets to Littleton, the more that changes. In fact, it was a horrific flood more than a half-century ago in June 1965 that spurred the building of the 1,500-acre Chatfield Reservoir in Douglas and Jefferson counties near Littleton, which was devastated in the long-ago flood. 

That flood stemmed from nearly stationary storms that dumped upwards of 14 inches of rain near Castle Rock and Deckers on June 14, 1965, according to a 9 News television report. With the South Platte River and Plum Creek swelling beyond flood stage, the waters began to spill over the bank and collect debris, according to Jenny Hankinson, curator of the collections at the Littleton Museum.

As a massive wall of water built and swept downstream towards Littleton, it began to grind everything in its path.

"With the force of the water behind it, it becomes a more powerful force," said Hankinson in the TV news report. "So, it is crushing things in its path and moving things in its path."

When the wall of water roared downstream through Littleton, Hankinson notes that 21 people died, 13 bridges were washed away, and more than 2,500 homes suffered destruction in a flash flood event that caused more than $500 million in damages, the equivalent of more than $4.1 billion dollars in 2020.

With 27 counties being declared disaster areas, the wheels were soon in motion to build Chatfield Reservoir, a project which was completed in 1975 thanks to a $74-million investment to build the flood-control and water-supply reservoir.

While reservoirs like Chatfield and others in the South Platte River system can help hold back flood waters, as well as provide the cold tailwater flow that has turned the region into a trout fishing destination, they can’t totally prevent events like this one.

A section of river with a jam-up of sticks, logs, and other detritus.
The Blitz Pool in Cheesman Canyon after the flash floods. (Pat Dorsey photo)

For now, Dorsey and others will have to wait to see the effects. The river in that canyon section will likely be in flux for a while, and as Dorsey noted, only time will tell its fate. 

It’s a sad development in a year that has seen its share of bad news surge through the fly-fishing world. Stay tuned at flyfisherman.com as we keep you updated on the latest developments on the nation’s most treasured trout waters.


Lynn Burkhead is a Senior Digital Editor with Outdoor Sportsman Group.

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