Raise your paddle overhead, parallel to the water, and pump it up and down. This can also be done by holding your arms out to your sides to form a "T" and waving them up and down slightly. The "all stop" signal is best used by a leader to warn followers about a potential hazard ahead. After the stop signal is shown, other paddlers should "wait for ‘all clear' before proceeding."
The universal signals can be used either empty-handed or with a paddle in hand. They are designed for high-visibility on the river, so always be sure to extend your arms as far over your head as possible so everyone can see. Once you see a signal pass it on so paddlers behind you will get the message. Boats nearby will be your quickest aid and you need to know how to signal them.
Raise your paddle blade (or a single finger) directly overhead, perpendicular to the water. For better visibility, turn the paddle blade flat to increase the surface area. Use the "all clear" to restart progress after a stop, or to direct the rest of your party to a preferred course (the best line through a rapid, for example, or around an obstacle). Lower the previously vertical ‘all clear' by 45 degrees toward the side of the river with the preferred route. Never point toward the obstacle you wish to avoid. Make everyone in the group understands this before you hit the water.
To signal distress on the water, you can either hold your paddle vertically and wave it back and forth; or do the same with a helmet, PFD, or a hand. If you have a whistle available, give "three long blasts" while waving to be sure you attract attention. The emergency signal, understandably, isn't set in stone, but as long as you signal with three whistle blasts and a wave you should be understood.
Repeatedly pat the top of your head to let the rest of the group know that you're OK and ready to continue on. These visual signals are designed to help paddlers stay in contact on the water and be safe when working their way through rapids. Keep in mind, however, that personal responsibility is still the key to safe paddling. Solid communication skills may help you out of a lot of sticky situations, but they are no substitute for knowing your limits and brushing up on those.