Tongue (V)
Also: tongue, V
The tongue is a smooth, V-shaped band where the main current flows between obstacles. It's usually the best line.
A V pointing downstream usually marks the passage between two rocks. A V pointing upstream, by contrast, indicates a rock just below the surface. Eddies often lie beside the tongue.
Sources and further reading
Research as of 13 Nov 2026. We have marked manufacturer information as such.