Guide To The Classification Of Rapids

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Whitewater kayaking is one of the most exhilarating parts of the sport of kayaking. Navigating fast-moving water, often filled with obstacles and drops, is not for the faint-hearted. The key to staying safe when tackling whitewater runs is to understand what you’re facing and know your own limits. To help you get an idea of the potential difficulty of a particular whitewater run, the American Whitewater Association has created the International Scale of River Difficulty.

While the ISRD isn't exact and isn't a replacement for the first-hand experience of the river, it does give you a good idea of what to expect, allowing you to prepare appropriately. To make things even easier, we've put together a list of essentials for whitewater running and broken down the ISRD to explain precisely what, in simple terms, the different classification of rapids represent.

The Classification Of Rapids

Class I:  

Class I rapids involve the fast movement of water, gentle rapids, and lighter riffles. There can be smaller obstructions to avoid, and self-rescue is possible, but not recommended. Despite the gentler nature of Class I rapids, a Personal Flotation Device (PFD) should be worn at all times. Class I rapids can be navigated using a sit-on-top kayak.

Class II

Class II rapids are fast moving and feature large waves and riffles. The channels and routes are usually clear and well-defined, and obstacles are generally easy to avoid. Because of the larger waves, we recommend that you use a sit-in kayak as opposed to a sit-on-top kayak.

Class III

Class III rapids are characterized by very fast moving water and larger waves. These waves and the swiftly moving water make Class III rapids more suited to experienced kayakers. There are strong currents, and this may cause obstacles to be harder to avoid. Kayakers will have to maintain a firm control over their kayak through stronger paddle strokes.

Because of the potential for larger waves and stronger currents, self-rescue is not practical. Kayakers attempting class III rapids should travel in groups of three or more to provide adequate emergency assistance.

Class IV

Class IV rapids have the potential to be extremely hazardous. Featuring rapid water movement, large waves, strong currents, and a large number of obstacles, they are suitable for experienced kayakers only. Strong paddling and boat control is necessary to navigate over larger waves and through features such as holes and drops. It is important that a kayaker has mastered the boofing technique to safely run Class IV rapids. Self-rescue is not practical, and most rescues will require a group effort and the correct equipment.

Class V

Class V rapids feature large drops, large waves, numerous obstacles, and should only be attempted by experienced paddlers in larger groups. Water currents and direction can be unpredictable, and there maybe be significant obstacles that need to be portaged around. When attempting Class V rapids, it is important to scout your route beforehand and have a good idea of the what obstacles you need to avoid.

Swimming condition in Class V rapids are very hazardous, and it's important you have a plan in place for rescuing a kayaker who has had to exit their kayak.

Class VI

Class VI rapids are the most extreme form of whitewater categorized. They often feature significant obstacles, large drops, and very fast-moving water. Only very experienced kayakers have the ability to run Class VI rapids, and even then at significant personal risk. Even when working as a group, rescue may be extremely difficult.

Whitewater Essentials

Regardless of the classification, running whitewater is always a challenging and potentially dangerous activity. Being properly prepared and having the correct gear will help you stay safe and get the most enjoyment out of the experience.


The first, and most important, step of any whitewater run doesn't involve a whitewater kayak. Before you get near the water, it is important that you do your research and know what kind of environment you'll be heading into. While the classification system of the ISRD can help, it's always a good idea to get advice from people with first-hand experience. Contact a local kayaking club or school and ask to chat with someone about the section of river you are planning on running. Most kayakers are eager to share their knowledge, and their experience could prove invaluable to keeping you safe.


A key factor to keep in mind is that river conditions can change significantly depending on a number of factors. When planning a whitewater run, it is vital that you understand how conditions will vary along the full length of the river. Weather is another important consideration. Water level changes caused by rain affect the whole range of the river and can significantly enhance the difficulty of a whitewater run. Keep an eye on the weather and remember, even if you're paddling under bright sunshine, rain further up the river can have a massive impact on your trip.


When surveying your potential route, keep in mind that most rivers have a number of obstacles, both man-made and natural, that you will have to account for. Man-made obstacles, in particular, can be a significant threat to kayakers and some, such as low-head dams, might not be immediately apparent. This video accurately demonstrates the danger of low-head dams, particularly to kayakers: 


While running whitewater require a range of skills, there are a few techniques that it are vital every kayaker knows and practices before heading out on the water.

The Eskimo Roll: One of the more important techniques for a kayaker to learn is how to roll your kayak upright if it has flipped over. Learning how to roll will allow you to bring your kayak quickly back to the upright position without having to perform a wet exit. Check out this video that covers a range of rolling techniques: 

The Wet Exit: If your kayak has rolled over and you find yourself unable to roll it back upright, it is vital that you understand how to perform an underwater, or "wet," exit. As most whitewater kayakers will be using a spray skirt, it is highly important that you understand how to get free of it during the wet exit. This video demonstrates the technique: 

Boofing: Boofing is a powerful forward stroke that allows the kayaker to run a drop without being caught in the hole at the bottom of the drop. Ideally, the boat stays flat throughout the maneuver and lands flat. Landing flat keeps the bow above the water and helps keep the kayaks forward momentum. This video highlights how to judge if you should be entering a hole and the technique needed to "boof" out of it: 


Bringing the right equipment with you is an important part of any kayaking trip, especially safety equipment. Some gear is optional or only useful in some situations, but the following are essentials that no whitewater kayaker should leave home without.

  • Personal Flotation Device (PFD): We recommend that you wear a PFD on any kayaking trip, but they are especially important if you are planning on running hazardous whitewater. Never leave home without one.

  • A Helmet: Running whitewater significantly increases the change that you are going to roll your kayak over or end up running into an obstacle, so it vital you protect your head with a good kayaking helmet.
  • Wetsuit or Drysuit: If you are planning on ‘yaking in cold water then it's important to dress appropriately. A wetsuit or drysuit will protect you from a range of debilitating conditions, from cramping to hypothermia. Remember to always dress for the temperature of the water, not the ambient temperature of the day.  
  • Emergency Whistle: Emergency whistles are small, easy to carry around, and can be attached to your PFD with a lanyard. Being able to attract attention in an emergency could save your life.
  • Rope: Throw ropes are an essential part of any kayakers safety kit, and can be used for everything from tying yourself onto an overturned kayak to pulling a stranded kayaker out of danger.
  • A Spare Paddle: Whitewater running can be tough on paddles, and not having a spare when yours breaks can quickly become a dangerous situation as you can no longer control over your ‘yak. An extendible paddle that can be kept inside the kayak’s hull makes an ideal spare.
  • Friends: When attempting to run whitewater, The American Whitewater organization recommends that you have a minimum of three people in your party and at least two vessels. Even low-grade whitewater can be significantly hazardous and there are some kinds of trouble you just can’t get yourself out of.

Staying Safe

There is no doubt that whitewater kayaking is a fantastic and exhilarating part of the sport, but

as with all extreme sports, it does come with an element of personal risk. The best way to enjoy whitewater kayaking safely is to use our guide and the ISRN to correctly understand what kind of situation you'll be facing on your chosen whitewater run.

If you do your research correctly, make sure you have the right equipment, and have mastered the necessary techniques, there should be no reason you can't make a whitewater run without undue risk. With the ISRD to guide you, you'll soon be boofing through holes and rock-gardens like a pro!

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