Fly Fisherman Makes Unusual Catch on Blue River

Colorado’s Blue River is famous for its exceptional year-round fly fishing. But when Jesse visited the river, he was shocked by what ended up in his net.
Blue River
Winter on the Blue River. Photo by © J. Peterson

Colorado’s Blue River is famous for its exceptional year-round fly fishing and abundant fish populations. The Gold Medal fishery provides anglers the chance to catch rainbows, browns and even the occasional brook trout, cutthroat trout and kokanee salmon.  But when Evergreen resident and avid fly fisherman Jesse Peterson visited the Summit County river, he was shocked by what ended up in his fishing net.

On Nov. 26, Peterson, along with his brother Zak, was fishing the Blue River in the popular tailwater stretch below Dillon Dam.  After a routine morning of landing several rainbow trout, Peterson cast a #22 black midge nymph into a deep pool and hooked into an unlikely specimen—a lake trout.  Peterson did an immediate double-take when the 15-inch, silver-colored “laker” appeared in the shallow water at his feet.

“I couldn’t believe my eyes,” said Peterson.  “At first I thought I had caught a brook trout but when I slid the fish into my net, I realized I had just caught a Mackinaw.  My brother and I have fished the Blue every year for the last 20 years and have never heard of anyone catching lake trout in this stretch of river, or in any river for that matter, not directly adjacent to the inlet of a large reservoir.”

15-inch Mackinaw
Angler Jesse Peterson landed this 15-inch Mackinaw (lake trout) while fly fishing the Blue River in the spillway below Dillon Dam on Nov. 26. Lake trout have never been stocked in Lake Dillon, which has raised questions as to why the fish have appeared below the reservoir’s spillway. Photo by J. Peterson.

Angler Jesse Peterson landed this 15-inch Mackinaw (lake trout) while fly fishing the Blue River in the spillway below Dillon Dam on Nov. 26. Lake trout have never been stocked in Lake Dillon, which has raised questions as to why the fish have appeared below the reservoir’s spillway. Photo by J. Peterson.

Lake trout, also called Mackinaw or “Macks,” are notorious deep-water dwellers. The fish live almost exclusively in the near-bottomless reaches of many of the state’s high-mountain lakes and reservoirs.Their necessity for cold, deep water makes the shallow, turbid environment of a river an unlikely and ill-suited habitat for the lake-dwelling fish. So how did this “Mack” end up in the Blue River?

Jon Ewert, Colorado Parks and Wildlife aquatic biologist, explains that although Peterson’s catch is highly unusual, it’s not unheard of for lake trout to occasionally occupy rivers.  Ewert says that CPW aquatic biologists discover a few rogue lake trout every year while conducting fish-population surveys.

biologists conduct fish-population surveys on a river
Colorado Parks and Wildlife biologists conduct fish-population surveys on a river. Photo by CPW

“Each time I electrofish the Blue below Dillon Reservoir, I always pick up one or two lake trout,” said Ewert.  “Because lake trout don’t do well in running water, these fish are usually emaciated or are in very poor body condition. Peterson’s fish is actually one of the healthiest I’ve seen.”

What makes this fish story even more interesting is Lake Dillon has never been stocked with lake trout. Ewert believes Peterson’s Mack strayed from its deep-water home in Green Mountain Reservoir and swam to the Dillon Dam spillway—an upstream journey of nearly 20 miles.

Located 20 miles north of Silverthorne, Green Mountain Reservoir supports an abundant population of lake trout and kokanee salmon. The salmon are the primary forage base for the lake trout, and Ewert speculates that lake trout may occasionally pursue kokanee into the Blue River inlet during the salmon’s fall spawning run.

“The kokanee in Green Mountain run all the way up to Dillon Dam when they are spawning, so we know there is ease of movement through the entire reach of river, said Ewert.  “Lake trout are likely following spawning salmon into the river and continue moving in the wrong direction instead of returning to the reservoir.”

Lake trout sightings in rivers are not isolated to the Blue.  Ewert says reports of river-bound “lakers” have become more common in the last year(2012), with fish showing up in some unexpected places.

“We’ve also found incidental lake trout in the Colorado River as far downstream as Radium, outside of Kremmling, so they’re capable of turning up in some far-flung locations,” said Ewert. “This year marks a high point for these types of reports that I’ve received, due to the huge volumes of water that spilled out of all our lake trout reservoirs in 2011.”

Because lake trout are ill-suited to survive in fast-moving water, Ewert says the predatory fish cannot reproduce and, therefore, pose no biological threat to a river’s ecosystem or to other fish species.

Jesse Peterson fly fishing
Jesse Peterson casts to feeding trout on the Blue River. Photo by Z. Peterson

For Peterson, this unlikely catch is simply an interesting addition to his fly-fishing resume´.

“I spend about 95 percent of my time fishing tailwaters, so this was my first ‘laker’ on a fly rod,” Peterson said.  “I still can’t really believe I caught it where I did, but it sure made for an unusual day on the water.”

Blue River Fishing Tips

Blue River rainbow
Caution: Slippery When Wet! Angler Zak Peterson displays a fat, Blue River rainbow. Photo by J. Peterson

You aren’t likely to catch a lake trout on your next fly-fishing trip to the Blue River, but you just might hook into a few good-sized rainbows or browns. Most fish average 16 inches in length, but brutes in the 4- to 6-pound range also occupy these waters.

Because of its proximity to Denver, the Blue River sees considerable fishing pressure.  As a result, the fish are wary and are highly selective (the resident trout are probably better than most anglers at recognizing fly patterns). No doubt, this is “technical” fly fishing at its finest.

Small midges and mysis shrimp fly patterns
Small midges (above left) and mysis shrimp are effective fly patterns for wintertime fishing on the Blue River. Photo by J. Neal/CPW

Bring a good assortment of mysis shrimp flies to match the “hatch.” Mysis patterns are most effective during periods of high flows out of Dillon Dam when the tiny, shrimp-like organisms are expelled into the river.  Midges are also a staple for wintertime fishing. Small flies ( #20 or smaller), 6X fluorocarbon tippets and a near perfect presentation are all necessary to trick the angler-savvy trout. Winter fishing is best midday into early afternoon, when water temperatures are warmer and insect activity is at its peak.

Note: Catch and release rules are in effect from Dillon Dam to the north city limits of Silverthorne (approximately three miles), and fishing is by artificial flies and lures only.

Article by Jerry Neal. Neal is the senior videographer and a media specialist for Colorado Parks and Wildlife. 

6 Responses

  1. We caught a laker while fishing the Blue below Dillon last summer. We were also surprised by this because we knew Dillon did not have lake trout. Thanks for the explanation. My fishing partner and I talked about this on the ride home.

  2. Thanks for your comment. We had a few questions as to how/why lake trout were showing up below Lake Dillon (as far as we know, a lake void of lake trout), which is why I wrote this story. Plus, it’s rare to catch a Mack on a fly, much less a small midge pattern. Even more unusual is that these fish, which are not at all suited for life in rivers, are making a 20-mile journey upstream from Green Mountain Reservoir. Thanks again for reading.

  3. Can’t say that I’ve ever caught a laker on a fly. I think I need to add this to my bucket list. Cool story.

  4. I caught a laker a few years ago on the South Fork of the Snake right below the dam. He was 20″ long and skinny as a rail.

  5. Was fishing the Blue right below Dillon with my son on July 13, 2018 and we were definitely surprised to see what we thought was a Mackinaw in the net. After getting home and doing some searching, we came across your article and felt even better about the unusual catch.

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