Supporting MCV has never been easier!

Contribute Now


Give a Gift Subscription

Update My Subscription

About MCV

Past Issues

School Resources

Contact Us

Annual report


Connect with us!

image of Facebook icon image of Twitter icon image of Google plus icon

Photo of Straight River.

Hungry for Hex

Come June, big trout rise to big flies in the heart of walleye country.

By Michael A. Kallok


The spruce and tamaracks that fringe the Straight River valley are brushed black and jagged in the stubborn twilight of midsummer. A band of coyotes greets the approaching night with a chorus of yips and howls, and I muster what remains of my willpower to resist the urge to cast.

"Be patient," says Bill Evarts, fisheries specialist in the Department of Natural Resources. "Wait for a fish to rise."

Free from the sweltering heat of the day, thousands of mayflies swarm above us. These aquatic insects likely emerged from the river a day or two ago and mated.

image of Hexagenia

Chasing the Hex

See video and images from the Straight River during the Hexagenia mayfly hatch.

map icon

View a map of the Straight River This is a PDF file. You will need Adobe Acrobat Reader to download it.

Now the females are making a gradual descent to the water to lay their eggs and die. In the parlance of fly anglers, this event is known as a spinner fall. But this is no ordinary insect. Roughly 2 inches long, these tawny brown and yellow members of the genus Hexagenia are the 747s of the mayfly world. And rivers where the conspicuous Hex and big trout converge command a lofty place in fly-fishing lore.

Oddly, the best place in Minnesota to experience this renowned hatch is far from the abundant trout streams of the southeast. This is why I'm fumbling through the dark in knee-deep muck in search of brown trout just west of Park Rapids with Bill and his wife, Edie Evarts, DNR assistant area fisheries manager. We paddled canoes to this spot, upstream from what locals call five-mile bridge. All six of the Straight River's road crossings west of town provide public access and are referred to by their distance from Highway 71.

For most of the season, solitude is easy to find on the Straight River, but "during the Hex hatch," Bill says, "you want to sort of stake out your spot early."

Cold-Water Anomaly.

We passed the hours watching swallows swoop and stab at a high-flying smorgasbord of winged insects. Near the water a cedar waxwing and a common yellowthroat made brief appearances as red-winged blackbirds called raucously from cattail tops. It's now 10 p.m. The incessant din of mosquitoes is accompanied by the ethereal call of a veery. Fifty yards upstream, the stark white light of Edie's headlamp pans the surface of the river.

"There are Hex on the water," she announces.

Less than 30 feet away from us, a sound like the splash of a golf ball confirms a large trout has also taken notice. Bill rolls out several false casts before sending his foam-bodied imitation of this oversized mayfly into the darkness. It lands softly, like a guess, and we listen anxiously for an answer. The Evarts share a passion for fly-fishing, particularly for trout. But when they arrived in Park Rapids for their new jobs in 2002, Bill admits the Straight River wasn't love at first sight.

At a glance, the Straight River hardly appears hospitable to trout. It cuts a sinuous course between cattail-lined banks that loosely define its soggy edges. From its origin at Straight Lake in Osage, this ribbon of water weaves a mere 17 miles through a broad, marshy floodplain before joining the Fish Hook River. It bears a striking resemblance to the nearby Shell River, which is home to warm-water fish like bass and pike.

What distinguishes the Straight River can't be readily seen. Its cold water is an underground anomaly, dealt by the shuffling and reshuffling of glacial material.

To the west and north of the Straight River are the hilly remnants of multiple glacial advances and recessions. Each period of melting delivered pulses of sand, gravel, and clay to the outwash plain. According to DNR area hydrologist Bob Merritt, this stacking of porous sand and gravel and nonporous clay resulted in a labyrinthine layering of aquifers. Springs occur where the river channel intersects the upper aquifer, and this influx of cold water accounts for at least half of the Straight River's flow.

Were it not for the Straight River's abundant springs, which provide oases of cold water, trout could not survive here at all. On the hottest summer days, water temperatures outside these cool refuges can exceed 78 degrees—approaching lethal levels for brown trout. Ironically, Hexagenia can proliferate in the Straight River because its water is slightly warmer than the streams of southeastern Minnesota.

Survival of the Fittest.

Whether this spring creek on the fuzzy border between prairie and forest was home to native brook trout remains a topic of speculation. DNR records from 1947 indicate brook trout were present in the Straight River, but they could have been stocked. Regardless, some believe intensifying agricultural demand for groundwater caused the river to get too warm for brook trout; others, like Edie, say the introduction of brown trout is the more likely cause behind the eventual disappearance of brookies.

By 1961, due to earlier stockings, records show the Straight River had become a mixed fishery of rainbow, brown, and brook trout. A 1976 survey turned up a healthy brown trout population. In 1980 the DNR stopped the occasional stocking of rainbow and brook trout. The DNR continued to stock brown trout until 1991, when it determined that natural reproduction was sufficient. Recent population assessments indicate brown trout not only thrive here, but they also commonly grow to lengths of 15 to 18 inches and occasionally exceed 20 inches.

The Straight River's trout have good reason to grow large: They find a diverse assembly of baitfish, including sculpin, dace, shiners, and chubs, as well as a good variety of caddisfly, stonefly, and mayfly species. Hexagenia nymphs spend most of the year tucked away in the sand and silt of the stream bottom. Typically, during a few weeks in late June, nymphs abandon their burrows en masse to begin the perilous business of metamorphosis. They swim to the surface and then pull free from their shuck. Drifting atop the water, vulnerable newly hatched adults unfurl and dry their gossamer wings before taking flight. Considering that one Hexagenia contains nearly as many calories as a small baitfish, the fleeting final chapters of its life cycle are, for trout, like an all-you-can-eat prime-rib buffet delivered on a conveyor belt. Not surprisingly, the period of fastest growth for the Straight River's trout coincides with the Hex hatch.

Trout and French Fries

The same groundwater that provides critical thermal refuge for the Straight River's trout is also important to the local economy. The valley's porous soils are ideal for growing potatoes, perfect potatoes—the kind fast-food restaurants demand to satisfy Americans' appetite for French fries. Cultivating these large, uniform, white spuds requires water, and the number of active permits for irrigation has increased in step with acreage dedicated to potato farming. In 1975 the river valley had only five active DNR-issued permits for irrigation wells. Today, more than 70 wells draw as much as 3 billion gallons a year to irrigate 9,200 acres of farmland between Osage and Park Rapids.

Advocates for the fishery have long feared that excessive pumping could reduce the groundwater flowing into the Straight River, thus raising water temperatures and lowering oxygen levels. In the mid-1990s, Trout Unlimited, the Minnesota Center for Environmental Advocacy, and the Headwaters Chapter of the Audubon Society filed suit to prevent the DNR from issuing new irrigation well permits. The lawsuit was settled in 1995 after the area's largest potato farmer and processor Lamb Weston/RDO agreed to help fund water monitoring. RDO also relocated its processing plant, cut water use for processing nearly in half, and designed the plant to reuse processing water for irrigation. Additionally RDO helped fund a comprehensive DNR watershed study. For purposes of the study, the DNR placed a moratorium on issuing new irrigation well permits in 1996, but it was lifted in 1998 after test pumping failed to produce sufficient evidence that agricultural irrigation put a significant strain on the Straight River's base flow.

Currently, the Straight River's brown trout population is healthy. But because of the complex, interconnected nature of the aquifer, uncertainty over how well trout might fare during drought remains. "What we have not seen is an extended drought with heavy pumping," Edie Evarts says, noting that more than a decade of above average rainfall likely recharged the aquifer. "The summer of 2008 was declared a drought, and the river stayed cool."

Fishing in the Dark.

Like other large mayflies, Hexagenia have evolved to emerge after sunset to conserve moisture and to avoid being devoured by sight-feeding predators. Brown trout are notoriously nocturnal, so this collision of survival strategies provides one of the best opportunities to fool a big Straight River brown. But as Edie points out, "Fly-fishing in the dark isn't for everyone."

"I'm in the trees," Bill mutters, eventually losing his fly in a game of tug-of-war with an alder. The commotion spooks the fish that had been rising, but several other trout have begun to feed noisily just downstream. We cast unsuccessfully until legal fishing hours end at 11 p.m.

Because bug activity during the hatch varies greatly from one section of the river to another, deciding where to fish requires an educated guess. Anglers generally think the Hexagenia hatch progresses upstream. So on the evening of the second day, we decide to access the river at the nine-mile bridge.

Cool air behind a front that swept a narrow band of thunderstorms across the region this morning is a welcome respite from yesterday's heat. But as the end of legal fishing hours approaches, it seems apparent that the Hexagenia will not appear tonight. Not a single fish rises, so we depart, pondering the vagaries of this giant mayfly's life cycle as we paddle upstream.

"That you, Bill?" booms an inquiry from behind a dense wall of cattails, as we nose our canoes around a tight bend through the lampblack darkness of a new moon.

"Yeah, is that you, Vern?" Bill calls back.

Vern Whitten, of Fargo, compares notes with us on the slow night, and we all paddle together to the bridge crossing where Whitten's RV is parked. There aren't any guarantees during the Hex hatch, so Whitten, who has been fishing the Straight River for 35 years, simply camps out for a week or two during the hatch.

Whitten, like other devoted Straight River anglers I spoke to, doesn't come here to catch a lot of fish. "It's a challenge and a mystery because there are big fish here, and they're really tough to catch," he says. "If you get one of those big ones on in the dark, you'll know what I'm talking about."

Premier Trout Waters.

Catching a Straight River trout isn't easy, and it became more difficult shortly after stocking ended in 1991. Hatchery brown trout released at road crossings tended to stay put, making them easy targets. Offspring from naturally reproducing brown trout spread out, seek heavy natural cover during the day, and are more wary than tank-reared fish. Today, Edie says annual electrofishing surveys indicate the Straight River's trout are larger on average and abundant in areas that offer suitable habitat. Still, there is a common opinion among local trout anglers that the population isn't what it used to be.

This change in perception, coupled with the Straight River's distance from major metropolitan areas, means its water gets little pressure from anglers. Although the river doesn't draw crowds, its aficionados speak of its charms, challenges, and need for continued stewardship with an evangelical zeal. One of the most outspoken is Ron Miller, a Fargo pediatrician who has spent nearly 30 years as a student of the river. It took five years to learn to fish the river well, he recalls.

"A lot of people come here and fish, and they struggle with it," Miller says. "It's a hard river to fish. You get caught up. You lose flies. So a lot of people give it up pretty quickly."

But Miller, who has traveled as far as New Zealand to fish for trout, says the Straight River is just as unique and challenging as some of the world's premier trout waters. His biggest trout, a 27-inch brown, came from the Straight River.

"It's a special place," he says. "Always has been; always should be."

While we chat, Whitten grills dinner for the half dozen friends who are lured here each year by the Hex hatch. Over burgers and potato chips, the anglers devise strategies for who is heading where. The names of their destinations hold no significance to an outsider. Yet one could guess that a particularly large male trout was hooked in the pool called "King's Hole" or that on a fine night in June, one might bump into Whitten on a river bend known as "Vern's Fish Factory." The Evarts, who have graciously invited me to tag along for a third evening, decide we are heading to "The Slot," a deep, narrow stretch of river flanked by thick growths of cattails—a likely spot for a big brown to lurk in the Straight River.

Deeper is Better

The Straight River's low gradient means the river struggles to move sediment. Because rain and snowmelt slip so efficiently through the sand and gravel of the Straight River valley, the river has no high-water events to force accumulated sediment downstream. Where sediment accumulates, primarily upstream of obstructions such as road crossings, the river becomes shallower, straighter, and wider. Water temperature increases at these wide, shallow stretches, which are bereft of trout habitat.

To address sedimentation, the DNR is working to replace undersized culverts at road crossings. It is also assisting with an innovative approach to help the river's wide, straight, shallow stretches become narrower, more sinuous, and deeper. In 2006 and 2007, the Headwaters Chapter of Trout Unlimited, with funding from the Straight River Trust, enlisted a helicopter to mimic a natural process of dead trees falling into the river. During the two-year pilot project, the helicopter dropped roughly 50 jack pines in wide shallow areas.

A tree strategically placed on one side of the river deflects water. When water is deflected, the river's velocity increases. This causes the thalweg, or deepest part of the channel, to move toward the bank opposite the tip of the tree, called the cut bank. Closer to the base of the tree, slower water allows sediment to accumulate and form a point bar. Eventually native vegetation crops up on the sediment.

Over time, as the cut bank erodes and sediment builds up on the point bar, the riverbed migrates laterally, resulting in a meander. The end result: a deeper, narrower, more sinuous river, which doesn't warm as easily and provides more thermal refuge during the hottest months as well as important overwintering habitat during the coldest months.

It's the first time a tree-drop restoration project has been employed on this scale in Minnesota, according to DNR river ecologist Neil Haugerud. In preparation for the project, DNR ecologists consulted the Michigan DNR, which has done similar restoration work on the Au Sable River, also well known for big trout and hatches of Hexagenia.

According to Haugerud, moderate width decreases and depth increases have already occurred in the project areas.

Static in the Dark.

As the sun creeps toward the western horizon, swallows feeding high in the air offer hope for a spinner fall. At 9 p.m. Bill and Edie paddle downstream to settle in to other promising spots and wait for the bugs to arrive. Up above, a loose swarm of Hexagenia appears like specs of static in the darkening sky.

The river has taken on the tint and texture of a blued gun barrel. On the otherwise silky water, I focus on a small dimple, and it suddenly transforms into a pair of upright wings. Soon, graceful sailboat-shaped forms are popping up everywhere, lingering briefly before taking flight.

Hex are emerging!

I clip the spinner pattern from my leader and select a pattern to imitate an emerging Hexagenia. As I struggle in the dark to tie a new knot, a pod of trout begins to feed enthusiastically. One leaps clear out of the water, as if paying tribute to this time of plenty with an elegant waste of energy.

A commotion downstream, sounding like a nervous puppy's first swim, precedes Bill's exclamation: "Fish on!"

Upstream, I count rings from four rising fish. Crouching down, I can see the profiles of emerging Hex as they drift through this gauntlet of hungry trout. Then a fifth trout begins to rise. With each concussive splash of this trout's rhythmic feeding, I can tell that it is much larger than the other four. The fish is inches away from the cattails, inconveniently behind a clump of branches. I err on the side of caution, and my fly falls short. But with the speed of a steel trap, one of the other trout grabs my offering. I lift the rod, and it comes alive, thrumming in my hand as the fish speeds upstream and then, just as quickly, downstream. In the dark, it's hard to anticipate where the fish is going. In the span of a minute, I clumsily bring an 18-inch brown trout to hand.

Meanwhile, Bill has just caught and released a 19-inch trout. He wanders upstream to check on me. We admire my fish under the light of our headlamps for a moment before it fins away.

Conspicuously absent now is the sound of feeding fish, so we again wait for a rise. The spinners that had been swarming above now blanket the water, but either spooked or full, the trout are silent.

"There was a big one up there, feeding right against the bank, sounded like someone dropping bowling balls in the river," I say.

"I know," Bill says. "Maybe you should call in sick tomorrow."

Learn more about the Straight River, its unique hydrology, and conservation efforts.

Looking for volunteer opportunities?