Backswimmers, Water Boatmen & the Trout That Eat Them

The strange little swimming insects nobody talks about enough—and how to fish them in lakes, rivers, and everywhere in between.

Somewhere in the world, a fly angler is standing beside a perfectly good trout river, staring into a fly box containing approximately $400 worth of meticulously designed imitations, trying to decide whether the fish want a size 16 Pheasant Tail or a size 18 Pheasant Tail.

Meanwhile, a trout just ate a bug that swims upside down.

Welcome to fly fishing.

We spend enormous amounts of time discussing mayflies, stoneflies, caddisflies, emergers, cripples, spinners, and whether a trout's refusal was caused by microscopic drag or our questionable personality. Yet an entire category of aquatic insects seems to have escaped the conversation.

Backswimmers and water boatmen.

You've probably heard the names. You might even have a few patterns buried in your fly box. But what exactly are these strange little creatures? Why are they so important in stillwater trout fishing? And perhaps most interestingly, what happens when you encounter them in a river?

Do you dead drift one? Nymph it under an indicator? Swing it? Strip it like a streamer?

And why does a Prince Nymph suddenly look suspiciously qualified for the job?

Things are about to get weird.

First, What the Heck Is a Backswimmer?

A backswimmer is an aquatic insect belonging to the family Notonectidae. It's a true bug, not a beetle, and it comes equipped with a streamlined body, two powerful swimming legs and a rather unconventional approach to life.

It swims upside down.

Not occasionally. Not because it's having a bad day. That's simply how it gets around.

Backswimmers are predators. They hunt other aquatic insects and sometimes surprisingly large prey relative to their size. They also possess piercing mouthparts capable of delivering a painful bite.

So if you find one, resist the temptation to pick it up and introduce it to your friends.

 

Their bodies also carry trapped air, allowing them to breathe underwater. That little silvery shimmer is important, because it gives fly tiers a useful clue about how to imitate them.

Now let's meet their frequently confused cousin.

Water Boatmen vs. Backswimmers: The Family Reunion Nobody Asked For

Water boatmen belong to the family Corixidae. They look similar to backswimmers, with oval bodies and oar-like swimming legs, but they generally swim right side up. Many feed on algae, detritus and tiny aquatic organisms rather than actively hunting larger prey.

Both can fly, both carry air underwater, and both can be found in quiet freshwater habitats.

 

For anglers, the most important difference isn't their Latin names. It's that both move through the water with little bursts of propulsion.

They're not mayfly nymphs clinging to rocks.

They're swimmers.

And that changes how we should fish them.

Why Lakes Get All the Attention

If you've spent time fishing trout lakes in British Columbia or Alberta, you've probably heard about water boatman fishing, especially during spring and fall.

These insects inhabit weedy shoals and shallow lake margins, where they feed, hide and periodically swim toward the surface to replenish their air supply.

In spring and autumn, adults may also take flight to disperse and reproduce. When large numbers are moving, trout can suddenly find themselves surrounded by tiny swimming snacks.

Imagine someone opening a buffet in your living room.

You weren't particularly hungry.

But now there's shrimp everywhere.

That's trout fishing.

The Freshwater Fisheries Society of BC describes these insects as an important stillwater food source and recommends fishing imitations through different depths, particularly around shoals and vegetation.

 

How to Fish Water Boatmen and Backswimmers in Lakes

Start around weed beds, shoals, drop-offs and shallow feeding areas. A floating line can work in very shallow water, but an intermediate sinking line is an excellent option when you want to retrieve your fly just beneath the surface or across the tops of weeds.

Cast beyond the feeding area, let your imitation sink to the desired depth, and begin retrieving it with short, deliberate strips. Try two or three inches at a time, then experiment with pauses.

Remember, these insects swim.

A perfectly motionless imitation might catch a fish, but when trout are actively hunting swimmers, movement often becomes the ingredient that makes the fly believable.

For deeper water, faster sinking lines can help you explore the water column. The trick is to retrieve through the depth where fish are feeding, rather than simply stripping your fly through empty water because that's where your line happens to be.

 

And here's an interesting thought: trout aren't necessarily eating these bugs because they look like a particular insect.

They may be responding to a small, dark, oval object that moves like food.

Which brings us to rivers.

The Mystery of the Backswimmer in a River

Here's where fly fishing gets interesting.

We traditionally associate rivers with mayflies, stoneflies and caddisflies. Our nymph boxes reflect that thinking.

But backswimmers and water boatmen aren't exclusively lake insects.

Both can occur in quiet areas of streams and rivers. Some water boatmen are genuine stream inhabitants, and certain species migrate into larger waterways to overwinter. Backswimmers can occupy stream pools, slow margins and eddies.

So imagine fishing a river like the Bow.

You've got beautiful riffles, long runs, deep buckets, back eddies, soft margins and sheltered pockets behind structure.

Would a backswimmer prefer the middle of a fast, turbulent riffle?

Probably not.

Would a quiet back eddy, slow shoreline, weed bed or protected pool make more sense?

Absolutely.

These insects are swimmers, but that doesn't mean they're immune to current. A backswimmer moving through slow water can suddenly find itself swept into a faster seam, where its swimming ability becomes considerably less impressive.

And there's our opportunity.

A backswimmer can be an active swimmer one moment and helpless drift food the next.

That suggests several different presentations.

Dead Drift, Nymph, Swing or Strip? Yes. But Not Randomly.

This is where anglers sometimes make fly fishing more complicated than it needs to be.

We want one correct answer.

One fly. One technique. One depth. One retrieve.

Unfortunately, trout haven't signed that agreement.

If you're fishing a faster seam downstream of a quiet pocket, dead-drifting a backswimmer imitation beneath an indicator makes sense. The insect may have been dislodged or carried out of its preferred habitat, and your fly can represent that helpless journey.

But what if you're fishing the quiet water itself?

Now we're dealing with an insect that can swim.

Try a short strip. Pause. Another strip. Let it rise slightly or swing across the current.

In slower pools, you might fish it almost like a miniature streamer. Cast across, allow it to sink, and retrieve with little pulses. Near a seam, a controlled swing can be effective, especially if you finish with a couple of short strips as the fly comes under tension.

The key is understanding what your presentation is trying to imitate.

Dead drift when the current is controlling the insect. Add movement when the insect is controlling itself.

These are fishing hypotheses rather than rigid rules. But they're useful ones, and they give you something far better than blindly changing flies every five minutes.

The Prince Nymph: An Accidental Backswimmer?

And yet it catches trout.

A lot of trout.

Now look at a beadhead Prince Nymph. Dark peacock-herl body. Contrasting white biots. Brown tail. Compact profile. A little flash and some movement.

Is it an anatomically perfect backswimmer?

Absolutely not.

But could a trout interpret it as a small swimming aquatic insect, especially when fished with the right movement?

There's a compelling argument for trying it.

In fact, Brian Chan's water boatman and backswimmer guidance for the Freshwater Fisheries Society of BC specifically notes that beadhead Prince Nymphs and Zug Bugs can fool trout during the early stages of insect flights, although fish may become more selective as they feed on the real thing.

So the Prince Nymph isn't merely a wild guess. It's a practical crossover pattern.

And it raises a bigger question.

How many flies in our boxes catch fish because they perfectly represent one named insect, and how many catch fish because they share enough characteristics with several different foods?

Perhaps trout don't read fly catalogues.

An inconvenient development for those of us who sell flies.

What Backswimmer and Water Boatman Patterns Should You Carry?

Purpose-built patterns generally feature compact oval bodies, swimming legs and sometimes a silvery or reflective underside to suggest trapped air.

Olive, brown, grey and black are useful colours, depending on the insects in your water. Sizes vary, so collect or closely observe local specimens rather than assuming every backswimmer is the same.

A dedicated water boatman or backswimmer pattern is an excellent choice when trout are feeding selectively. But a Prince Nymph, Zug Bug or other compact, dark, slightly flashy nymph can provide an effective searching option.

Don't overlook the presentation.

A perfectly tied imitation stripped at the wrong depth can be less convincing than a generic fly moving exactly where a trout expects to find food.

That's fly fishing in one sentence.

Unfortunately, it doesn't fit very well on packaging.

The Next Time You're on the River, Look Somewhere Different

The next time you're fishing a trout river, spend a few minutes looking beyond the obvious riffles.

Check the slow shoreline. Watch the weeds. Study the back eddies and soft pockets where current and quiet water meet.

You might discover an entire little ecosystem that you've been drifting past for years.

And if you see a small insect paddling around upside down, don't immediately assume it has experienced a catastrophic navigational failure.

It might be a backswimmer.

It might be trout food.

And it might explain why your Prince Nymph just caught a fish when nothing else was working.

The wonderful thing about fly fishing is that every time we think we've figured it out, the river introduces another variable.

Sometimes that variable is a tiny aquatic predator that swims upside down, carries its own air supply and bites people who get too curious.

Nature has a sense of humour.

Apparently, so do trout.

 

The FishFuel Takeaway: Fish the Behaviour, Not Just the Bug

Backswimmers and water boatmen remind us that choosing a fly is only half the equation. Where the insect lives, how it moves, how it becomes vulnerable and where trout intercept it are just as important.

Try a Prince Nymph. Experiment with a Zug Bug. Carry a few dedicated boatman and backswimmer patterns. Fish them dead-drifted, swung or retrieved when the water and insect behaviour justify it.

And when you finally catch that trout on a Prince Nymph, feel free to tell everyone you perfectly matched the hatch.

We won't tell them you were fishing a fly that might represent six different things.

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