Wildfire is key for fish health, scientists say.
Words by Clayton Franke
Photos by Jeremy Williams

Following an afternoon float on the McKenzie River in Western Oregon, fly fishing guide Clay Holloway cleans his drift boat at the Helfrich boat launch. His cheeks are slightly sunburnt — it’s still early enough in the summer season that he hasn’t quite developed a full tan.

Sporting flip-flops and khaki pants, he wades into the river, dips a plastic jug into the current and sloshes water over the inside of the boat, washing mud and grime down a hole in the floor. He just guided two clients down one of the most heavily burned stretches on the river near the town of Blue River 51 miles East of Eugene. In Sept. of 2020 the 173,000 acre Holiday Farm Fire turned lush cottonwood and Douglas fir to wooden skeletons, vibrant ferns to a dry, crumbling forest floor, homes to solitary chimneys, and cars to molten masses of metal, glass and rubber.

As he gears up for the summer tourist season, Holloway’s only concern is that the altered scenery along the river might deter some clients from booking trips. The new trees and debris in the river presented a few obstacles on the float, and Holloway noticed some areas are now harder to reach because of it. For McKenzie River wild rainbow trout, it’s just what they need, and Holloway said the fishing was still good. 

The flames that bring such destruction to human life and property are key to building diverse habitat for wild rainbow trout, a fish deeply intertwined with the people and ecosystems of the McKenzie river. The wild trout’s resilience serves as an ecological reminder of wildfire’s permanence and the potential consequences of human intrusion. 

A drive East along highway 126 along the McKenzie River reveals several clues of the rainbow trout’s significance in the area. Mailboxes dotted along the road are decorated with wooden trout silhouettes, painted with the trout’s characteristic red stripe. Then, there’s the town of Rainbow, named after the trout, at mile marker 47, where flames from the Holiday Farm Fire nearly scorched the town. Here, fish and fire exist harmoniously, while McKenzie River communities struggle somewhere in between, adoring one and fearing the other.

McKenzie River rainbow trout are native to the Columbia River basin, and they’re found in rivers across the Pacific Northwest. Nicknamed the “Redband” trout, the fish boast a prominent bright-red stripe across the broadside of their bodies and rosie red cheeks. Hundreds of small black spots cover their dark emerald green backs, which helps them camouflage within the McKenzie streambed, protecting them from osprey and hawks above. The trout’s appearance resembles its environment, one molded by fire.

As the Holiday Farm Fire moved west through the McKenzie River corridor, its flames singed trees and bushes along the streambank. Scalding red embers danced and fluttered across the river, igniting the opposite bank and surrounding the river in flames.

While an inferno raged above, trout hid below the water’s surface in deep pools, safely away from the heat. Unlike other wildlife, a trout’s habitat within the stream isn’t at risk for destruction from flames themselves.

Instead, it’s debris flows that can be dangerous, said Becky Flitcroft, a fish biologist for the US Forest Service. A large mass of soil, sticks, rocks and trees crashing down burned hillsides into a stream is the most likely reason for fire-related fish death.

“It’s coarse material, fine material and trees and everything that was along the way,” Flitcroft said.

After a year of heavy rain, Oregon Department of Geology landslide experts like Bill Burns grow particularly concerned about destructive debris flows. Increased water content in hillsides makes them heavier and more likely to slide. Burns recorded a debris flow earlier this year in a steep channel near Quartz Creek. Luckily for the residents with homes still standing along the McKenzie, this winter didn’t bring as much rain as usual. The homeowners can breathe a sigh of relief -- but for fish, landslides can also a post-fire gift.

At Finn Rock Landing on the McKenzie, where flames burned both sides of the river, a tangle of charred and broken wooden debris hugs the north bank. Near the upstream side of the tangle, the crown of a Douglas fir dips into the water column, leaving the blackened trunk stretching to its former place on the bank, where its needles used to shade the water.

Now, the tree’s bare branches create a web of broken sticks and bark, casualties of a fire-decimated forest. Behind the pileup, the current slows. White and yellow foam dips and swirls, then kicks upstream, caught in an eddy.

It’s the perfect place for a trout to feed and escape from predators, and from Holloway’s drift boat.

Towards the middle of the river, as the McKenzie charges towards its confluence with the Willamette River, the water starts to chop and bob, indicating the presence of a gravel bar. Wild rainbows splash at the surface every few minutes to feed on passing insects. Then the current speed slows dramatically and the water plunges into a deep pool, and the color darkens to a point where, despite pristine water conditions, the streambed seems miles away.

When a slide enters a river, the current goes to work — sediments initially affect water quality, but eventually get sorted out. Heavy logs and large boulders don’t move far, while fine sediments tumble in the current until they settle in slow-moving water. Intermediate, gravel-like material usually settles in under a riffle, creating prime real estate for fish to lay eggs.

Fish bury their eggs in the gravel on the bottom of the stream, in a riffle, like the one at Finn Rock. This way, the eggs aren’t exposed to predators like Bull trout and other rainbows. When they hatch, they can flee to the pool below.

“The river is always moving material. If you don’t add material, the river is just going to sweep it clean,” Flitcroft said. “That complexity of gravels, fine material, wood and all of those things that provide cover and food sources and habitat will eventually just get washed away. So, getting these inputs of sediment and material over the long term are really important for a fish.”

River sediments contain nutrients such as nitrogen and phosphorus. Jana Compton, an Ecologist for the EPA, said these nutrient levels are lower in late summer. When landslides deposit material into the stream, nutrient levels spike, fueling the aquatic insect life that provides food for trout. According to a study from Ecohydrology, changes in stream nutrient levels after a fire usually leads to an increase in size and growth rate of trout.

That’s good news for the recreational fisherman who flock to the McKenzie each summer, and for those whose livelihoods depend on wild rainbows.

Holloway remembers catching his first wild trout on a fly rod near Blue River as a ten-year-old. Before that, he had only caught stocked hatchery trout. He remembers being surprised by the strength and power of the wild fish shaking and thrashing at the end of his line, a feeling that makes the McKenzie special for many anglers.

Holloway makes most of his living guiding on the upper river above Leaburg dam, which is managed for wild trout. The stretch from Leaburg dam downriver to Hendricks bridge is stocked with hatchery rainbow trout from Leaburg hatchery at river mile 38. The difference in fish is significant, especially when it comes to dealing with fire.

The genetics of wild rainbows are specifically tailored to their environment and to survive massive disturbances like the Holiday Farm Fire. A 2015 study from Freshwater Science journal examined wild rainbow trout populations in the Boise River watershed. In streams that burned and had debris flows, juvenile rainbows reproduced earlier in their life cycle than in streams that didn’t burn.

This is a major reason why wild rainbows are so resilient. After a disturbance event, juvenile rainbows respond by rebuilding the population. Before then, “nobody ever knew that they had this adaptation to local catastrophic events built into their physiology,” Flitcroft said.

It’s an adaptation that wild, native rainbow trout have developed throughout their existence in the Mckenzie River. On the other hand, Flitcroft said, non-native and hatchery might not be adapted to fire disturbance, especially if the hatchery fish aren’t genetically similar to the wild, native fish.

Erik Whithalm is the manager of Leaburg hatchery. As the fire approached the hatchery, the Eugene Water and Electric Board opened the Leaburg dam in fear of clogging it with fire debris — the same kind of logs that build fish habitat. Whithalm was forced to release over a million rainbow trout and salmon from the hatchery as the water levels in his ponds dropped.

He said Leaburg hatchery uses a Cape Cod stock of rainbow trout spawned at the Roaring River hatchery near Albany. According to the Oregon Department of Fish and Wildlife Hatchery and Genetic Management Plan, the Cape Cod stock was delivered to Washington from a commercial hatchery in Massachusetts in 1942, and later distributed in Oregon. The plan also says “no significant alterations have been made” to the stock since it was delivered to the Roaring River hatchery.

This means rainbow trout from Leaburg hatchery share little genetic adaptation with natural Mckenzie river rainbows, making them more susceptible to death from landslides or stream restructuring. The genetic difference is beneficial for keeping wild fish wild, because they are less likely to breed with hatchery fish. However, it doesn’t bode well for the hatchery fish who had to navigate the Holiday Farm Fire or for the fish released unexpectedly.

As Holloway’s drift boat slides through the riffle at Finn Rock, the patchy whizzing of a chainsaw slices through the meditative bubbling, rushing and splashing of the river. Holloway says he can’t quite get used to the noise when he’s on a float.

The chainsaw noise comes from multiple salvage logging projects on the banks of the Mckenzie. ODFW fish biologist Jeff Ziller has been advising the Oregon Department of Transportation on these cleanup projects. He says ODOT has removed logs from the banks that would’ve provided fish habitat. “We let them know we weren’t terribly happy about that,” Ziller said.

These projects use heavy machinery to drag logs across the unstable banks of the McKenzie.   According to fire ecologist Tim Ingalsbee, this creates a disturbance to the watershed that’s more harmful than the fire itself.

“Forests and watersheds evolved with recurring fires,” Ingalsbee said. “They didn’t evolve with commercial industrial logging or fire suppression.”

With the trees downed, the McKenize’s newly bare banks allow more sunlight to hit the river, potentially warming water temperatures, especially in smaller streams that flow into the McKenzie. Warmer streams means less dissolved oxygen in the water, a detriment to cold-water species like trout. Lower snowpack in the mountains due to climate change means the river reaches dangerously low — and thus warmer — levels in late summer.

As temperatures warm, wild rainbow trout face other problems caused by climate change.

Studies have found that a pattern of uncharacteristic wildfires due to climate change could jeopardize the resilience of native fish to fire. The window for wildfire ignition in the summer is widening due to climate change, which could mean more frequent wildfires, and less time for fish to respond. But it’s an open question as to how that might impact wild rainbows in the McKenzie River. “What that means for our fishes and aquatic ecosystems, I don't know,” Flitcroft said. 

Holloway depends on the health of the McKenzie river’s wild rainbows, and in turn, depends on the wildfire that supports their life cycle. He’s been fishing here his entire life and seen the river change day-to-day, month-to-month and year-to-year. As fire regimes change, so does the natural cycle of the river, and it’s unclear what that means for the McKenzie.

But even with jumbled messes of debris lying on the banks of the river, Holloway says he appreciates the new landscape.

“It’s still beautiful, just in a different way,” Holloway said of the McKenzie’s changed landscape. “That’s up to interpretation.”