An opening or openings where water can flow through, but a solid object such as a person or boat cannot. Usually formed by trees on the banks, or by rocks on top of one another with water flowing through them. One of the most dangerous river features.

A Guide designated to oversee the smooth running of a trip.

, excerpted from “Whitewater Rafting,” by William McGinnis. 

A section of river that can be boated.

River access where a trip begins.

River access where a trip ends.

Moving water.

The right side of the river when facing downstream.

The left side of the river when facing downstream.

The “steepness” of a river, measured in feet of elevation loss per mile of river.