Okay, But What Kind of Class IV?

What separates Class IV from Class V isn't wave size. It's what happens when you're out of the boat. 

The more whitewater I run, and the more river trips I manage, the less useful I think the Class I through V rating system gets.

Not wrong. Just thin.

We run everything from warm, mellow, family-friendly floats to the Murtaugh, which is about as advanced as commercial rafting gets in Idaho. Large day-trip operations out of Riggins. Big multi-day trips on the Salmon. I've trained over a hundred river guides.

And across all of it, the most common way a guest describes their experience is the same four words.

"I've done Class IV."

Okay. What kind of Class IV?

First, credit where it's due

The rating system works. It has worked for sixty-seven years, which is longer than almost anything else in this sport.

American Whitewater's membership built it in the 1950s so that kayakers and open canoeists could compare rivers they hadn't seen. That was the job. It does that job well enough that every guidebook, every permit, every insurance form, and every rafting website in the country is written in its language, including ours.

Charlie Walbridge has run American Whitewater's safety program for five decades and is still credited on the current version of the code. Here is what he says about the scale he helped maintain:

"Rivers are too complex to simplify into a number."

That's not me taking a shot. That's the guy who wrote the thing.

I got the same message from a completely different direction recently. I met up with Paul Primus and got a behind-the-scenes tour of the Boise Whitewater Park, checking out the hardware that shapes those waves. One line of his has been rattling around in my head ever since. I'm going from memory rather than a recording, so I won't put it in quotes, but he said something along the lines of:

We know more about spaceflight than we do about river hydrodynamics.

That's coming from someone who builds waves on purpose, with engineered flow and adjustable equipment, in a controlled channel in the middle of a city. If moving water is still that hard to predict under those conditions, we should probably go easy on the idea that one Roman numeral can describe eighty miles of wild river.

If you want the actual class-by-class definitions, we already wrote that one: the full Class I through VI breakdown. This isn't that article. This is the one about what happens when you try to use that number to run a company.

What I actually want

I'll be honest about where I've landed.

As somebody who manages a river company, I kind of just wish we had a three-point scale.

One: you'll be bored. Totally safe. Beautiful. Bring the grandparents.

Two: you'll be stoked. Big fun water. This is why people drive four hours.

Three: you'll be scared. You could get hurt. You probably shouldn't be here.

That's it. That's the whole scale.

Obviously that's a joke. It's also the exact problem I want to spend the rest of this article on, because those three levels squeeze difficulty and danger into a single number, which is the thing the class scale already does and the reason it can't tell you what you actually need to know.

But I'm not the only one who's felt the pull. AVA Rafting in Colorado quietly stopped leading with class numbers for their customers and built a nine-level scale instead: Leisurely, Fun and Mellow, Splashy and Moderate, Exciting and Active, Thrilling and Very Active, Wild and High Exertion, Heart Pounding, High Intensity, Maximum Adrenaline. Their reasoning was that they wanted "a single system that we feel is accessible to our guests."

A real outfitter looked at Class I through VI, decided it didn't communicate, and shipped a nine-point feelings scale.

I wanted three. They built nine. Somebody else built forty-two, and we'll get to them.

Class 4 vs Class 5 rapids: what the numbers actually say

Here's the honest comparison, straight from American Whitewater.

Class IV is "intense, powerful but predictable rapids requiring precise boat handling in turbulent water." Risk of injury to swimmers is moderate to high. Group assistance for rescue is often essential.

Class V is "extremely long, obstructed, or very violent rapids." Eddies may be small, turbulent, or hard to reach. And the line that matters most: "swims are dangerous, and rescue is often difficult even for experts."

Read those again and notice what actually separates them. It isn't wave height. It isn't how scary it looks from the bank. The escalation from IV to V to VI is written almost entirely in terms of what happens to a person who is out of the boat and how hard they are to get back.

Most people rating rapids never get that far down the page.

One more thing almost nobody knows: American Whitewater rewrote the scale in 2024. The new version dropped Class VI entirely. It dropped the plus and minus modifiers. It dropped the 5.0, 5.1, 5.2 decimal system. Their own wiki still serves the old version with all three.

There are two live versions of the International Scale on the internet right now, and they disagree.

That alone should tell you how much precision to expect.

Auger Falls at 21,000 cfs. What would you rate it?

What the number was never built to carry

Go read the actual class definitions and start listing what isn't in them.

Gradient isn't in there. Not once. Volume isn't in there. There is no cfs figure, no unit, nothing. Two rivers at 800 cfs and 80,000 cfs can carry the identical rating. Water temperature isn't in there. Undercuts aren't in there. Sieves aren't in there. Wood isn't mentioned. Neither word appears anywhere in any class definition. Remoteness isn't in there. Portages aren't in there. Whether the run is pool-drop or continuous isn't in there.

And here's the part every outfitter should know by heart. The 2024 code says, in writing:

"These guidelines are not intended to serve as a standard of care for commercial outfitters or guides. These guidelines are for informational purposes only."

The scale isn't failing. It's being asked to do a job it politely declined.

Idaho examples that carry the same number.

Big water: the line is easy, the swim is not

On June 1, the Salmon River at White Bird typically runs about 37,700 cubic feet per second. On August 15 it typically runs about 4,980. In a big year, June 1 is closer to 75,000.

Same river. Same rapids. Same canyon. Same published class rating.

At peak, the waves through Ruby and Lake Creek get enormous. And a lot of experienced people look at that water and say it's straightforward. Point downstream, hit it square, hang on. They're right. In the boat, it's the best day of the season.

Lake Creek at 54,000 cfs

Out of the boat is a different sport. The eddy lines are powerful, the water boils, and it's a long way to anything that stops you.

The rating has no way to say that. It says Class III to IV in June and Class III to IV in August, and those are not the same trip.

Worth saying plainly, because we sell this water: I don't actually think guests are shopping to flip. What they want is to feel like they're right on the edge of it. Thrilled, soaked, laughing, gripping the line. Not swimming. Big wave trains sell the feeling of jeopardy without much of the jeopardy, and that's a real product, and there's no number for it.

You can watch the flows for yourself on our live Salmon and Snake River conditions page, and our Riggins day trips run that water all season.

Technical water: the guide is working, you're bored

Flip it around and you get the opposite failure, which almost nobody talks about. Most of the summer the Middle Fork runs at low volume. That is a real Class IV and it takes years to be good at. Constant reading, constant correction, picking a line through rocks four inches under the surface, moving the boat two feet left because that's the difference between clean and pinned. A guide down there is working the entire time and is genuinely gripped in places. And the guests are bored. No big waves. Nobody's getting soaked. Nothing looks like the photos they booked off of. Somewhere around hour three you get some version of: what's the big deal here? Why do we keep paddling? Where's the whitewater? Same Class IV. One person in that boat is at the edge of their ability and the other is wondering when lunch is. The number described the water correctly. It just described it to the wrong person.

Our own Snake River run, where we round up

I'll use ourselves as the example so nobody thinks I'm pointing at a competitor.

American Whitewater rates our Hagerman section of the Snake as Class II to III. Our website says Class III. Are we lying? No. There are Class III rapids in there and we run them all day. But we picked the top of the range, the way everybody in this industry picks the top of the range.

The number misses in the other direction too. Hagerman runs around 5,000 cfs year-round because it's dam-fed and spring-fed, which is real volume for water that looks this friendly. Big fun wave trains all summer, everybody laughing, and it's genuinely rare for anyone to come out of the boat. But if you do go in, it isn't the gentle bathtub swim a Class II implies.

Family water, and more push behind it than the rating lets on. Both true. One number to say it.

The same rapid, two different rivers

Flow is the biggest thing the class number ignores, and Idaho has the cleanest examples in the country.

Slide Rapid on the Lower Salmon, in American Whitewater's own words: "barely a riffle at 10,000 cfs to class V at flows above 20,000 cfs." One rapid. One name. Four class numbers depending on the day.

Traps Creek on the Riggins reach runs the other direction. It washes out at most flows and becomes the hardest rapid on the section at low water, getting harder as the river drops below 4,000.

And the Murtaugh, which American Whitewater describes:

"The character of the river and lines through the rapids change dramatically with flows... Murtaugh is often described as three rivers in one, because of its three inner canyons that are either exposed or inundated as flows change."

Three rivers. One rating. And the direction of the change is the same everywhere:

More water moves the difficulty from your hands to your lungs.

Low water is technical. You work constantly, and a mistake costs you a bruised shin. High water is easier to steer and much harder to survive. A rating that can't tell you which side of that trade you're on is describing a river you haven't been told about.

Our French Creek base camp trips say Class IV in June and Class III+ by late summer on the same page, for the same water. We're not being inconsistent. We're just admitting the number moves.

It cuts both ways, and that's the part people miss

Everybody assumes a bigger number means more danger. It doesn't reliably work that way in either direction.

Blossom Bar on Oregon's Rogue River is Class IV. One of the outfitters who runs it says his clients come through and go, "Wow, that's it?" People wearing life jackets have died there. There's a sieve on the backside called the Picket Fence that takes things in and doesn't give them back.

Dimple Rock on the Lower Youghiogheny is Class III. A paddler describing it years ago: "My word, it looks like a class II- rapid if one stays right." It is severely undercut, it has killed repeatedly, and a coroner's jury eventually recommended stronger warning language for rafters.

That's the whole problem in two rapids. A Class II can have a strainer, a sieve, or an undercut in it that will kill you, and the class number gives you no warning at all, because none of those words appear anywhere in the scale.

This isn't a hunch. A 2020 study in Wilderness and Environmental Medicine went through the American Whitewater accident database back to 1950. In the Southeast, Class I and II water accounted for the single largest share of whitewater fatalities, at 32 percent. In the Rockies, Class IV led at 38 percent and Class I to II was 12 percent.

Be careful with that number, and I want to be careful with it here. There are vastly more people floating easy water than hard water, so raw counts aren't rates and I'm not telling you Class II is more dangerous than Class V. What I'm telling you is that the things that actually kill people on rivers, which are no life jacket, wood, low-head dams, cold water, and long swims, are not what the class number is measuring.

And it runs the other way too. A rapid can look genuinely terrifying from the bank and be reasonably rated lower, because it has a clean runout, catchable eddies, and a swimmer gets picked up promptly. By the letter of American Whitewater's own definition, that's not Class V, no matter what it looks like in the photo. The scale asks about consequences. Most people rate on appearance.

Two very different sentences that sound identical

Here's the version of this that actually matters when somebody calls us.

"I've rafted Class IV" and "I'm comfortable swimming Class IV" are completely different claims, and almost everyone says the first one while I'm listening for the second.

Plenty of people do not have the fitness, the whitewater experience, or the composure to swim a Class IV rapid. They'd have a miserable time in that water. And that is completely fine, because they can absolutely book a multi-day trip with Class IV rapids on it and have the trip of their life, riding in a boat with a guide who runs a smooth line.

Those two things are both true, and the class number can't hold them at the same time. It describes water. It doesn't describe whether you've ever been in that water with your helmet on backward and your paddle gone.

So when somebody tells me they've done Class IV, the useful follow-up isn't "which river." It's "did you swim, and how did that go."

And then there's "I'm a Class IV guide"

This one will get comments, so let me be precise.

I'm not saying guides are overrating themselves out of ego. I'm saying the same number is quietly doing two completely different jobs.

"This is a Class IV rapid" is an adjective. Nobody measured it, nobody signed it, and nobody can revoke it.

"I am a Class IV guide," in a system that means something, is a credential. The International Rafting Federation's Level 4 raft guide award requires fifty logged runs or a hundred hours guiding on Class IV or harder, a scored assessment on a written skill sheet, on a river of verified class, with a current first aid certificate, expiring in three years. Their trip leader award at that level wants a hundred and twenty-five runs or two hundred and fifty hours.

We run every guide through our own bootcamp using IRF-inspired benchmarks, and here's my honest read after doing that for years. Most of the people who call themselves Class IV guides can absolutely run Class IV. They read water, they pick lines, they get down the river clean, day after day. That part is real.

The gap shows up when it goes wrong.

Flipping a boat back over fast, with cold hands, while it's still moving. Getting a swimmer who has stopped listening back to the raft. Counting heads. Giving directions to another boat that's about to make the same mistake you just made. Deciding in four seconds whether to chase the person or the boat.

That's a different skill set, and it's mostly fitness, drilled repetition, and leadership. It's why we default to lead guides when things go sideways, and it's why we spend two to three weeks a year on training before the season starts.

Most of it comes down to one thing we probably don't do enough of as an industry: guides need to swim more rapids.

Not fall out of boats. Swim them, on purpose, in control, until it stops being an event. There's a rhythm to it that you only learn by doing it a lot. Knowing when to relax and let the river carry you, conserving air and energy instead of fighting water that's going to win anyway. And then knowing the exact moment to stop being passive and go, hard, because that eddy is the one you're grabbing. That's not something you can pick up from the boat.

Class IV describes the water a guide can run. It says nothing about the day a guide has to manage when it stops going according to plan.

Here's the detail that convinced me this confusion is real and not just my pet theory. In 2016, the International Rafting Federation renamed its own award tiers from "Class" to "Level," specifically to stop people confusing them with the river classification system.

The profession found the collision confusing enough to change its own paperwork.

People have tried to fix this. It goes badly.

I'm not the first person to notice any of this, and the graveyard is instructive.

In 1998, American Whitewater seriously considered adding a danger rating. Letter designations. X marks on rapids where people had died. A parallel one-through-five scale just for hazard. They said publicly that they'd build it if there was demand. There wasn't enough, and the community decided prose descriptions of hazards were better than another number.

A canoe club in Ohio went the other way. In the mid-1970s, two NASA engineers named John Kobak and Dick Priem built a forty-two-point river rating system scored across ten weighted factors, including ease of rescue, inaccessibility, continuousness, and water temperature. It's genuinely thoughtful. It's still maintained. On it, the Nantahala scores 19 and the Ocoee scores 25, and both of those are Class III, which tells you something real.

It's also used, as far as I can tell, by approximately one canoe club. And the weights that turn ten factors into forty-two points were never published anywhere.

An outfitter in Washington built a risk matrix instead: probability times severity, one through five on each axis, twenty-five possible outcomes.

So the options on the table are one number, forty-two points, or a twenty-five-cell matrix.

The sports that solved this didn't add complexity. They added exactly one thing. Climbers separated how hard the moves are from how bad the fall is, and Scottish winter climbing uses two numbers where the whole message is the gap between them: one route is technically hard and safe, another is technically easy and will kill you. Avalanche forecasters keep terrain and daily conditions as two separate published ratings and refuse to combine them, because one changes on a decade scale and the other changes overnight.

What I'd actually propose

Fair warning: this is a proposal, not a standard. Nobody has adopted it. I'm not claiming they should. It's just an idea to discuss. I manage a rafting company, not a governing body.

Keep the class number. Add one thing, and always say the flow.

Class III+, Swim 4, at 38,000 cfs.

The class tells you how hard the rapid is to run. The Swim Score tells you what happens to the person who ends up out of the boat. And the flow, because none of it means much without the flow.

Roughly:

Swim 1. Warm, short, ends in a pool. You're back in the boat before you've finished being surprised.

Swim 2. Warm enough, some push, maybe a spin. Most people are laughing by the time they're back in.

Swim 3. Long enough or cold enough that it stops being funny. You'll probably collect a bruise. The boat has to come get you and you'll be glad when it does.

Swim 4. Powerful water, long hold-downs on eddy lines, a long way to anything calm. Real potential for a hard hit. This is where practiced rescue skills stop being theoretical.

Swim 5. No reliable recovery before the next thing. Cold, continuous, or violent enough that the swim itself is the emergency.

What moves that number on a given day: water temperature, how far to the next pool, whether the eddy lines will hold you, how much rock you're going to make contact with, and whether there's a known entrapment hazard anywhere in the runout.

And notice that two of those run in opposite directions, which is exactly why one number never worked. Low water means more rock and shorter swims. High water means fewer rocks and longer, colder, more powerful ones. Entrapment doesn't follow either one. Foot entrapment mostly happens in waist-deep water on rivers nobody's worried about.

Here's where I'd break from how we handle class ratings, though. The Swim Score isn't a permanent property of a rapid. It's a number for today.

Avalanche forecasters worked this out decades ago. They rate the terrain once, because terrain doesn't change, and then they publish a separate danger rating every single morning, because the snowpack does. They deliberately refuse to combine the two. A rapid's class can sit in a guidebook for thirty years and still be roughly right. What a swim costs you there changes with the flow, the water temperature, and whether there's a new log in the wrong place.

Here's what that looks like on water we actually run. These are examples of how the idea would work, not published ratings of anything.

Where	Class	Swim	What the pair says
Hagerman, summer, most of the run	II to III	2	Family water with more push in it than the number suggests
Riggins, mid-August, around 5,000 cfs	III+	2	Warm, playful, forgiving. The kind of swim people retell at dinner
Riggins, late May, around 50,000 cfs	III+ to IV	4	Same rapids. Cold, pushy, a long way to anything calm
The flat water between rapids, Riggins at 50,000 cfs	II	4	Nothing to maneuver around. Boils, whirlpools, and eddy lines that don't let go
Snow Hole, Lower Salmon	IV	3	You'll swim to a pool, but through powerful swirling water and some small holes on the way
Slide, Lower Salmon, above 20,000 cfs	V	4 to 5	Extremely powerful eddy lines. Expect long hold-downs. American Whitewater's number, not mine

Read the two Riggins rows against each other. Same reach, same rapids, same published class, six weeks apart. That's the whole article in one table.

And notice the Lower Salmon appears twice with two different numbers. A seventy-two mile trip doesn't have one swim number any more than it has one rapid. The brochure gets one anyway. Now look at that fourth row, because it's the one that breaks my own pattern.

Every other line in this table has the swim number more or less shadowing the class number, which is a fair criticism of the whole idea. That row doesn't. The water between the rapids at Riggins at peak flow in May is Class II by any honest reading. Nothing to maneuver around. No waves worth naming. A guest would call it the calm part.

It's also boiling. It's full of whirlpools and eddy lines that will hold somebody down and spit them out a hundred yards from where they went in. Swimming there is a Swim 4 in water a guidebook would call a II.

And the most extreme version of this isn't on our rivers at all. Low-head dams sit on Class I and II water all over the country and account for roughly one in ten whitewater fatalities. That's a Swim 5 on water nobody would rate above a II.

That's the whole argument, and it isn't about the Class V rapids. It's about the flat spots.

For multi-day trips I'd add one more number, stated once for the trip instead of per rapid: how hard it is to get help. The Riggins day trip runs along a highway most of the way, so a bad afternoon means a short scramble to a road. Below White Bird, the Lower Salmon is fifty-three roadless miles and the only way out is a boat. Same river. Same class rating. Completely different plan when something goes wrong.

And then I'd stop. Every attempt to bolt a fourth number onto a rating system in any adventure sport has quietly died from neglect. Canyoneers added an optional risk rating twenty-five years ago and their own community now says it "means very little," because optional numbers stop getting filled in.

So what should you actually tell us?

Don't lead with the class. Tell us any of these instead:

• What river, what section, what month

• Roughly what the flow was, if you happened to look

• Did you swim any of it, and how did that go

• Were you paddling, or riding in an oar boat
  

Or just skip all of that and tell us what you're after. Did you want a big wild ride? Did the boat flip, or did you come out of it, and was that the best part of the day or the part you're still thinking about?

Any one of those tells us more than the number does. If you swam a big-water Class III in cold water and got yourself back to the boat, that's worth more to me than a Class IV you rode through in August. Either way we'll put you on the right trip. And if you'd rather know what a swim is actually like before you find out, we wrote about how to swim a rapid too.

The Class I through VI scale isn't broken. It's a good tool built for a specific job by people who told us, in writing, that it wasn't exact.

We're just asking it a question it was never given the vocabulary to answer.

See our day trips · Or step into a multi-day Salmon River expedition

Frequently Asked Questions

Are Class 4 rapids dangerous? Class IV rapids carry risk of injury to swimmers, and American Whitewater's definition notes that group assistance for rescue is often essential. On a guided commercial trip the guide runs the line, so the practical risk to a guest depends more on water temperature, flow, and how long a swim would last than on the class number itself.

What's the difference between Class 4 and Class 5 rapids? Class IV is intense but predictable and requires precise boat handling. Class V is longer, more violent, and more continuous, with small or unreachable eddies. The real dividing line in the official definition is not wave size, it's that Class V swims are dangerous and rescue is difficult even for experts.

How hard are Class 3 rapids? Class III means moderate, irregular waves and some real maneuvering, with complex moves in fast current. For a guided raft guest it is genuinely exciting and usually forgiving. Big-water Class III on a high-volume river can have larger waves than a technical Class IV on a small one.

Does a rapid's class change with water level? Yes, sometimes by several classes. American Whitewater describes Slide Rapid on Idaho's Lower Salmon as "barely a riffle at 10,000 cfs to class V at flows above 20,000 cfs." Some rapids get harder as the water drops rather than rises. Always ask about flow, not just class.

Who decides what class a rapid is? Nobody official. American Whitewater publishes the scale and maintains a river database, but ratings come from paddlers, guidebook authors, and outfitters, and the scale's own text warns that "regional or individual interpretations may cause misunderstandings." There is no governing body that assigns or certifies a rapid's class.