IN NORTHWEST WISCONSIN — Rivers paddled at night focus the senses. Water laps more loudly than in daytime. So too the wails of coyotes and songs of sedge wrens, whose callings pierce the dark, like thunderclaps.

Also, by seasons, trout otherwise hidden beneath the surface tip up their noses to sip flies, an action that resonates stereophonically in the dark.

Late Thursday evening, Dave Zentner and I slipped our canoe quietly into one of many rivers that twist and fall across far northwest Wisconsin, not far from Lake Superior. These are waters, often, that divide vast sloughs, draining cedar bogs and tag alder swamps. The most famous is the Brule, a river fished by five presidents. Tonight Dave and I are on a smaller stream, brought here, each of us, by the hatch, erratic as it's been this summer, of Hexagenia, or "Hex," a mayfly.

In the north country, the Hex bears the weight and importance of life itself. Trout need these flies to gain weight, often putting on as much as 25 percent of their annual chubbiness in the three weeks or so the Hex is present.

Also, cedar waxwings chomp on these flies, as do turtles, frogs and blackbirds, each a part of a life mix that begins and ends, fundamentally, with clean, cold, flowing water.

"It's a night-by-night thing, the hatch, particularly this summer," Dave said. "Let's see what happens."

Dave lives in Duluth, an hour or more distant from this river, and is among a fairly small legion of conservationist-nutjobs who can't quite get enough of river fishing, fly rod in hand.

Dave's wife, Margo, an apparent saint, will tell you her husband comes and goes with the season's hatches, sneaking at all hours from the house with a canoe on top of his truck, and other gear inside, not least boxes of flies and fishing memories dating back six decades.

In spring, Henricksons are among the first flies that gather Dave's attention, followed by caddis and stoneflies, then brown drakes and, finally, the Hex.

The Hex is noteworthy because when it's present, monstrous trout often rise to the big Hex imitations anglers deploy, and because (see above) night fishing focuses the senses in ways few other experiences do.

Headlamps are required here, also depth-charge-size cans of mosquito dope, patience, too, and not a little humility, in that anglers often cast flies to trout whose locations can only be estimated.

"There's a rise," Dave said.

He's in the stern, I in the bow, and we angle the canoe quietly to the right side of the stream.

Now in his 70s, Dave has been doing this since the 1950s, evidence that the attraction between him and night fishing for trout never has been fully sated.

"That's a good fish," he said, assessing the tenor of the splash.

As he spoke, Dave, a lefty, loosened a couple of rod lengths of line, looped the line ahead, false cast once and delivered his fly against the opposite bank, watching as the river current carried it downstream.

Nothing.

Again, Dave put his line in the air, dusk now morphing to nighttime, 10 p.m. well and gone.

This time as the fly drifted, the river boiled beneath it. Instantly, Dave reefed back on a brown trout that, when brought alongside the canoe, pushed 19 inches, thick around the girth, too, a real specimen.

"That's quite a fish," I said.

"Quite a fish."

We pushed downstream, gently paddling. But the night was not unfolding as we wanted. We saw very few Hex duns on the water, the stage of the fly that appears on the surface briefly before becoming airborne.

More unfortunately still, no spinner fall was occurring, this last marked by the falling of Hex flies that, having risen from the river and mated, die and fall back to the river, triggering, usually, a hellacious trout bite.

Around shadowy river bends, alert for the sound of trout rising and the sight of spinners falling, we paddled. We saw none of the latter but intermittently detected the former, taking turns casting as we did.

This small-stream traveling at night presents its own form of trout fishing, particularly so on a river marked by so many deadfalls. Casting 7-weight rods with heavy, short leaders, the undertaking, in boxer's terms, is less light-footed punching than stand-and-slug.

"Once you hook up, you need to keep the fish out of the brush," Dave said. "Sometimes you have to 'horse' them in to do that, which is why we use the heavy leaders."

My biggest trout of the night I fooled when darkness had so overcome us I could have cast no less effectively with my eyes closed.

Lying in wait, unspeaking, we were pushed up against the left side of the river, our paddles in the soft river bottom, holding the canoe in place.

Downstream, a muskrat broke the river surface gently, plying his trade. Otherwise, save for the laughing of distant coyotes, and the occasional bark of a hen mallard, the evening was as quiet as it was black.

Then, upstream, we heard a splash that registered high on the Richter-like scale Dave uses to gauge the size of rising fish.

"Good fish," he said.

Deftly, like assassins, we back-paddled against the current, hugging the river's edge, until we were slightly upstream of where we had pinpointed the rising.

Again we waited.

And waited.

Hearing no more risings, I looped a blind cast into the darkness, judging the drift of my fly intuitively.

Fishermen, real fishermen, measure time not in minutes, hours or days but in trips past and future, and those under way.

It was 1 a.m. when we pulled the canoe from the river, strapped portage wheels beneath it and toted it over a very long stretch of swamp grass to Dave's truck.

Into the black night we drove.

As we did, I thought about that trout, imagined how big it was, and thought, too, that I should have set the hook more quickly.

Maybe then, in the dark, I would have fooled the fish. Instead, he fooled me.

Dennis Anderson • danderson@startribune.com